You got some pretty bad answers to this question, which is no reward for your curiosity, so I thought I'd give it a go.

The unit rosters in Total War games are generally based on troop types and specific named units attested in the sources. For some in-game factions, a great many historical unit types are known, leading to well-rounded rosters (Rome or Seleukids for example). For many others, though, we have little to no specific information about the historical nature of their armies. In those cases, the game developers default on a couple of standard "cultural" unit rosters that generate a distinct combat style. This is why all the Gallic factions, for example, or all the Persian factions, have basically the same unit selection available to them.

Now, the Greeks had settlements all over the Mediterranean and the Black Sea, and the conquests of Alexander spread further Greek-speaking settlements all through the Near East. The result is that there are a great many Hellenic factions in the game. However, only a few of those factions were actually important players on the geopolitical stage in the period in which the game is set, and for the great majority of them, we lack specific details about the nature of their military forces. They therefore default onto the Greek "cultural" unit roster, which is mostly based around hoplites, some weak skirmisher units, and light cavalry. The game designers clearly had a lot of fun trying to create variations within this default set, with semi-barbaric Massilian and Cimmerian hoplites, thureos and thorax variations based on the introduction of new technology, and the like. But fundamentally, a lot of these hoplites are a placeholder for information we lack.

There is, however, some justification for the choice. As far as we know, all Greek city-states used hoplites as the heavily-armed backbone of their armies throughout the Classical period and beyond. Despite a good deal of local variation in fighting styles, the hoplite really was widespread, at least in the Aegean, Sicily and Southern Italy, Cyrenaica, and the Black Sea coast. Why was this?

The main thing to bear in mind here is that these communities didn't have a free and unlimited choice of what troops they could raise. Most Greek city-states were small communities with limited public finances, and they did not get to be picky about what they wanted their armies to look like. They relied for their defence on a mass levy of their citizens, and those citizens turned up with whatever weapons they could afford. Since the spread of hoplite equipment in the 7th-6th centuries BC, those who could afford such equipment would turn up as hoplites. Those hoplites would then band together to form heavy infantry formations, which formed the core of most city-state armies.

It's not their effectiveness, then, that made hoplites so common. Rather, they were widely used because they were widely available, and for many states, they were all that was available (along with the rest of the levy, who fought as cavalry or light-armed troops). They were the citizen body in arms, and they were all a city had to defend itself in wartime. Indeed, Total War games tend to distinguish between weak Militia Hoplites and somewhat tougher Hoplites, but in reality this distinction did not exist; all hoplites were militia hoplites (unless they were mercenaries; see below). At best, a city-state could field more specialised units of heavy infantry by selecting the toughest or fittest from the general levy and forming them up separately. This is represented in the game by the availability of units called Picked Hoplites and Light Hoplites (both of which are historically attested). In the game, these are distinct troop types; in reality, they were just subgroups of the hoplite militia.

So why did all these Greek levies use the same equipment? Unfortunately, the rise of the hoplite is obscured by the mists of time; we have no narrative account of the period when this particular type of heavy-armed warrior came to form the backbone of Greek armies. The distinctive piece of kit that made a man a hoplite (the round, bowl-shaped, double-grip shield called the aspis) appears on vase paintings for the first time around 730BC, but the cost of the armour meant that it was at first only available to the richest Greeks. It's not until the middle of the 6th century BC that we see the first mass hoplite armies, with thousands of hoplites fighting side by side in formations from which light troops and horsemen had been excluded. By that time, hoplite armour had already spread all through the Greek world. The exact reason for its popularity is unclear. However, it's worth noting that the equipment is not so distinct from that used by many Near Eastern peoples around the same time, suggesting a general shift towards close combat tactics within a broader cultural zone in the period c. 800-500 BC. Unsurprisingly, later Greek sources don't see any problem referring to Egyptian and Assyrian infantry as "hoplites".

So why did the Greeks, perhaps even more so than their neighbours, embrace heavy infantry fighting styles? My theory is that it was the best way to make mass citizen levies effective. These people were just ordinary citizens, without training and without much military experience; the Greeks recognised that such troops couldn't be any good with missile weapons or on horseback. How does one make the most of a force of eager, but untrained warriors, whose main strength is not skill or expertise, but sheer valour in defence of their homeland?

Hoplite tactics completely omit any form of skill or sophistication, relying entirely on the courage of each hoplite and his willingness to close with the enemy. Hoplites didn't skirmish, manoeuvre, feint or fall back; they simply lined up and charged whatever they found in front of them. It was the best way to use the particular skill set of heavily armed but poorly trained warriors. This was how Greek city-states, who could not afford to raise professional armies, were able to defend themselves against outside forces.

The Greek victory against Xerxes (480-479 BC) confirmed this approach; through their aggressive tactics, the clumsy militias of Greece had managed to defeat the largest and most professional army in the world. Meanwhile, even though hoplites had already been hiring themselves out as mercenaries before that time, the practice really took off during the Classical period, as states and peoples with less effective heavy infantry of their own (like the Thracians or the Persians) took advantage of the growing mercenary market to supply themselves with an effective troop type. For them, hiring hoplites was a conscious choice - although perhaps one that had less to do with the particular effectiveness of hoplites and more with the fact that Greek mercenaries were freely available. These mercenaries, on account of their long service, were able to increase their tactical abilities and effectiveness, even though they broadly retained the simple and aggressive approach to battle that had made them famous. Their superiority to militia hoplites made them desirable even to city-states, who began to complement their hoplite levies with mercenary hoplites if they could afford it. The result was that hoplite fighting styles spread even further across the ancient world, to the point where there were more hoplites in Persian service against Alexander than Alexander himself brought along from Greece.

After Alexander's conquests, hoplites and hoplite-based armies gradually faded from view, as large states with bulging treasuries were able to focus on raising and training any troop type they liked, rather than relying on poorly trained militias or money-hungry mercenaries. The superior training and tactical ability of the Macedonian pikeman drove the hoplite into the margins of warfare even in the Greek world. Interaction with Celtic peoples introduced the Greeks to the thureos shield, which allowed them to turn the hoplite into a lighter, more flexible warrior type. With the rise of Rome, fewer and fewer of the states that still relied on their own hoplite militias still had an independent foreign policy, and by the beginning of our era the hoplite had more or less disappeared.