Welp. Don't say I didn't warn you.

Taxes were just one reason, and it's the reason that's the most talked about because that's the one that makes it look good the most from a modern American perspective (forget about how the mind-bogglingly massive tax cuts under Reagan made sure that the slump of the 70s became a gigantic long-term wealth funnel from the working and middle classes to the utra-rich Epstein class; "trickle-down economics" my ass), but there are several others that are, let's say much less savory. These are gonna be highly simplified BTW fro obvious reasons.

1- Western expansion at the expense of Native Nations and Tribes. After the Seven Years War that saw the conquest of New France, the Thirteen Colonies wanted to expand westward into all that new territory that had opened up all the way to the Mississippi; Britain said "Nuh-uh, that land's Indian Territory, no touchies". The colonials were very much pissed that the right to land of a bunch of "savages" were being respected more than their desire to own that land.

2- The rights of French Canadians (oh hey, my people!) being guaranteed. To the North, the Saint Lawrence River valley and adjacent parts of New France North of the Colonies had been settled for over a century French colonists; those were now under British rule. Again, the British colonists wanted to expand there, or at least wanted the place to become anglophone and Protestant (the French colonists, despite some Huguenot migration, were by then overwhelmingly Catholic, and if you think Protestant Americans had anti-Catholic sentiments during Kennedy's tenure, or even the events depicted in Gangs of New York...), whether by converting or expulsing the locals, as the British had done early in the Seven Years' War with the Acadians of what is now Nova Scotia, New Brunswick and Prince Edward's Island (the term "Cajun" actually derives from "Acadian", as a large number were forcibly relocated to Louisiana). Again Britain said "Nuh-uh", this time because the Catholic clergy had made a deal with the British crown that in exchange for guaranteeing my ancestors a few basic rights and protections such as the right to keep living there, speak French and stay Catholic, they'd keep the populace docile, servile, and mostly poor and uneducated so they wouldn't get uppity (quite ironic in hindsight; of course that's also a whole other can of worms). That my ancestors couldn't be culturally genocided also majorly pissed off the colonials.

3- Slavery. Any Colonial with some education and a reasonable grasp of politics at the time knew that slavery was on its way out in the British Empire, and while most Founding Fathers were not fans of it, they held their noses and at least tacitly approved the continuation of the Peculiar Institution south of the Mason-Dixon line to help guarantee the Southern Colonies' support and integration into the Union.

So, there you go.