Perhaps I do not need TurboTax, but I know that the laws at the state and federal level change every year and that I have no real ability to track any of this, but the penalties can be high for failure. I rarely understand tax jargon, in any case; I always feel like I am on the back foot of some "clever" debate team tactic of convenient definitions.
So, aside from just the lobbying aspect -- which is not trivial -- I would say that the general terror of the IRS (Al Capone, after all, fell to them), the shifting territories of tax law, and the jargon barriers also contribute to keeping TurboTax in business.