Greetings! Thanks for asking the "bigger question" of the USA entering the First World War, though if I may be a tad blunt, I would put forth that the "commonly cited" reasons OP has included in their explanation came from either tertiary sources (documentaries, textbooks, and the like). Most academic treatments on the United States' experience of the First World War do not focus heavily on the sinking of the Lusitania (which by the way, occurred 2 years before the U.S formally entered the war) or the Zimmerman Telegram. For example, here is a recent lecture given by American First World War historian Michael S. Neiberg on the reasons for America's entry into the war, in which he spends a grand total of about 10 minutes on the Telegram and even less on the Lusitania (a good lecture on the whole by the way, so definitely worth a watch.)

I know this question is probably pretty controversial, but let me know if you can answer this question for me. I'm guessing there's an economic reason behind it. There usually is.

This question, to reassure OP, is anything but controversial, and the heavy focus on either the Lusitania or the Zimmerman Telegram is actually something that historiographical narratives of America's war have pretty much dismissed since the 1960s/70s. Popular history however, seems to still have a ways to go. Regardless of that, let us see if we can shed some light on the events, concepts, and contributing factors which led to the American entry into the Great War. Note that this response is what I like to call a "Frankenstein response" in the sense that it is made up of bits and pieces from various other related AH threads I have weighed in on. Those original threads are linked at the bottom in the "Sources" section, so feel free to peruse those writings for further reading. Preamble and plug aside, let's begin.

Neutrality and the New World (1914-1916)

When war was declared in 1914, America followed its foreign policy of "isolationism", in which it generally frowned upon and refused to take part in European affairs, especially if those affairs involved a conflict. This war seemed to be no different at the outset, and as a result the American public was overwhelmingly in support of neutrality. President Woodrow Wilson was not exactly passive in this regard either (that is, he did not simply declare US neutrality and leave it at that). He monitored the war as it unfolded "across the pond", and in 1916 his personal emissary Colonel Edward House attempted to explore the possibility of an Allied-German peace settlement, with America mediating the two sides. This of course, was not possible in a year which had seen so many (at least superficial) German victories on both the Western and Eastern Fronts, and would not satisfy the Anglo-French terms of peace either.

The American public itself was also divided by 1916. Whilst Wilson believed that "British navalism" was just as bad as "German militarism", there were two clear sides forming (albeit minority sides, as neutrality remained the major sentiment up until 1917). On the one hand, America was full of ethnic German-Americans, whose vote Wilson may have wished to secure by promising neutrality in the coming years. There were also Irish voters in the Eastern cities, whose fury at the British oppression during the 1916 Easter Uprising meant they were against the US joining an old enemy. On the other hand, the Pro-British side was formed of the "Wasp" (White Anglo-Saxon Protestant, as Michael Howard terms it) supremacy on the east coast, as well as notable figures such as newspaper magnate William Randolph Hearst and ex-President Theodore Roosevelt. Neither side could claim the majority up until 1917, so America had to remain politically neutral in the whole affair.

Yet whilst America remained neutral, there were certainly events which pushed it towards intervening in the war. Namely, as the war dragged on, the American public became more and more aware of various atrocities committed by the German forces in their occupation of Belgium and their deliberate destruction of places of cultural heritage, such as the destruction of the Belgian town of Leuven in August of 1914, alongside its esteemed University Library. Further, German unrestricted submarine warfare was causing considerable nuisance to America's flow of trade, but by no means was it (yet) substantial enough to cause Congress or indeed Wilson to push for war. When the Lusitania was sunk and 128 American lives were lost, there was an uproar in the public and the government, but it was moreso over the legal consequences of the sinking rather than the sheer loss of life (one should hasten to add here that other American lives had already been lost in Europe as a result of the fighting). Washington seemed more adamant to prove that the Germans had torpedoed a neutral merchant vessel in direct and egregious violation of international law, and the Germans for their part attempted to prove that the Lusitania had not been a neutral merchant liner. The main (substantiated) part of their case rested on the fact that the British liner had been carrying munitions in her hold, though both the Cunard Line and the American government considered this point moot in the purview of international law (feel free to ask a follow-up question on the Lusitania business, as there is a fair bit to analyse but that digresses from our point here).

What the outrage over the Lusitania did spark however, was the decision by Germany to restrict its submarine warfare. Keep this development in mind, as we shall return to it in the later part of the response.

The Economic Argument

I'm guessing there's an economic reason behind it. There usually is.

10 points to OP! There was indeed an economic reason behind the US entering the First World War, but do not be swayed into thinking that it actively got involved in order to expand its economic interests or purely to enhance its economic power in the world. Economically, America was most certainly not neutral prior to 1917, though this was mostly due to wartime fact rather than commercial preference. France and Britain relied to a considerable extent on shipments of American goods to sustain the war effort, and the US was more than willing to extend credit to these countries and continue the flow of materiel. On the other hand, the Royal Navy's blockade of Germany meant that no US goods were able to flow into that country. This of course created a natural "tilt" towards the Entente Powers, and gave the traders in America more to worry about as the war dragged on. Michael Howard sums up this economical perspective well:

"Yet as the war went on an increasing amount of that business [America getting involved in war] consisted in supplying war material to the Allies - not necessarily out of ideological sympathy, but because they could not get it to the Germans. If that trade were interrupted, then the war would become their business, whether they like it or not."

This fear of interrupted trade had been realised in 1915 when the Lusitania was sunk. Though she had been carrying ammunition in a secret hold compartment, the Germans were forced to scale down their submarine offensives in the Atlantic and operate by "cruiser warfare rules", by which all passengers had to be warned of an attack, allowed to abandon ship, and pointed in the direction of the nearest port (idealistic at best, downright impossible and impractical at worst).

With the recent historiographical work on the matter, we now know that key advisers and business officials in America did indeed share concerns about a German victory endangering the economic expansion and security of the United States. In the 1920s and 1930s, "revisionist" and "New Left" historians contested that the economic security of the United States, coupled with the threat to that security posed by German unrestricted submarine warfare, led the American government to choose intervention over neutrality.

Part 1 of 3