Are we sure? No. Herodotus is quite truly the only surviving detailed source anywhere near contemporary with the Persian invasions of mainland Greece, and it is often impossible to tell whether later ancient sources had other sources or repeating Herodotus if they do not contradict his Histories. For the sake of a loose citation, almost all of the information about Xerxes' preparations for war come from Book 7. There are inconsistencies in Herodotus' report. He says that the original pontoon bridge was destroyed, and then describes the final product that Xerxes actually crossed as constructed from war ships - triremes and penteconters - rather than some more mundane type of cargo ship or barge. There's also the issue that no mainland Greeks ever saw the bridge with their own eyes. According to Herodotus' narrative, the bridge was destroyed while the army was still in Greece and by the time the Greek allied fleet arrived in the region a year later, it was already gone.

That said, there's not any significant reason to doubt the story. As you mentioned in the OP, the Achaemenid Empire was perfectly capable of organizing large building projects, and actually made a habit of it. In addition to the examples you mention above, referenced by Herodotus, the Achaemenid Empire had a series of well organized bureaucracies managing building projects including, Mesopotamian canals, routine temple restorations across the empire, royal palaces in the heartland, defensive structures and garrisons on the northern and western frontiers, and state run agriculture to support the nobility and government officials.

It also has to be noted that Xerxes' army was working within a very specific context. Herodotus famously exaggerates the size of the Persian army, claiming 2 million soldiers, their horses, baggage train, and 2 million camp followers to an army that was at most 200,000 people total including non-military participants. Even at middling estimates closer to 100,000, it still represented the largest plausible military force ever assembled (at least in the Near East/Eastern Mediterranean). The logistics alone were extraordinarily complex. Herodotus describes an army gathering with the king and marching west through Anatolia as well as a second force that marshaled to the south and joined the king at Sardis after marching up the Mediterranean coast.

Once in Europe, it had to be split into three separate columns, each resting and resupplying at different cities and depots in Thrace to avoid placing too much burden on any one site. Even then, Herodotus describes the Persian army as devastating the local resources in several places. Historian's also speculate that one of the reasons King Alexander I of Macedon warned the Greek alliance not to try and halt the Persians in the Vale of Tempe was simply to keep the Persians moving and out of Macedonian territory as fast as possible.

This would be one reason to construct the pontoon bridge as well. In the aftermath of the invasion, first when Xerxes' personally withdrew with the bulk of the army and again when Artabanus led the retreat from Plataea, the Persians suffered from the utter lack of resources left in the region after they passed through the first time. In all likelihood, the original plan involved either wintering over in Greece or being resupplied by the Persian fleet, neither of which was possible after the defeat at the Battle of Salamis. Instead, Herodotus reports the Persian army becoming increasingly starved and exhausted as they waited for ships to shuttle them across the Hellespont and Bosporus. The full army massed all in one place put such a drain on resources, that it was logistically impossible for them all to wait at Abydos and Sestos while the army crossed, but if any one contingent moved ahead without the whole force, they'd just end up stacking up in Macedon or some other rendezvous point for an extended period of time anyway.

One factor that emerged soon after Xerxes' Invasion, but was a constant concern for later empires was trade between the Black and Mediterranean Seas. In the early Fifth Century BCE, this trade route was still in its infancy. Trade between Greek and Thracian cities around the Black Sea was mostly limited to the Greek and Phrygian territories in Anatolia, under Persian rule. In Xerxes' time there's even some debate over whether or not the Persians simply ruled all of the major Black Sea ports outright, or at least controlled enough of their trade to have de facto control. So not only was trade through the Sea of Marmara less significant, but the Persian Empire could dictate policy for most of the parties involved regardless. Within a few decades, partially due to the end of Persian naval dominance after the Battle of Salamis, trade through the Hellespont increased dramatically.

Herodotus already describes how Xerxes' pontoon bridge had to have a system for raising and lowering boats to make way for trade ships to pass by. As the value and quantity of shipping increased over the decades and centuries after the pontoon bridge, it would have been increasingly difficult and undesirable to block off a major commercial artery for extended periods of time, and both Herodotus's direct statements and the logistics describe indicate that Xerxes intended his pontoon bridge to last for at least two years. Later empires' logistics actually benefited from this trade network as well. As more grain and other foodstuffs flowed out of the Black Sea, more could be made available to any military force operating along the coasts.

Xerxes' invasion also occurred at a unique moment in Achaemenid military history. They had uncontested naval supremacy in the eastern Mediterranean, with no fear (at the start) of an enemy counter attack on the pontoon bridge. Immediately following the Battle of Salamis, that advantage was wiped out forever, and few if any armies crossing the Hellespont in later history ever shared it.

Few forces from the empires you listed in the OP ever had similar conditions to motivate the construction of a pontoon bridge. Black Sea shipping became too valuable. Naval dominance was often contested. The supply-line problems faced by Xerxes' were never as severe for other conquerors on account of both smaller armies and increased availability of resources. Some of the examples you listed, like Alexander, the Crusades, and the Romans have their own extenuating circumstances. Neither Alexander nor the Crusaders intended to return by the same route any time soon after embarking. Alexander set out to conquer as far and wide as he could, while the Crusaders intended to take and hold the Levant. Rome's first invasions of Anatolia were facilitated by the bequest of Asia Minor by Attalus III, giving them a large staging ground to build up and expand through a combination of minor conflicts punctuated with major gains.