A counter viewpoint - maybe the system has to be complicated to provide all the various incentives that voters want taxes to do, and to patch all the loopholes that would otherwise be open. Maybe such a system is too complicated for a lay person to understand so they delegate the understanding to private enterprises which can compete to provide the cheapest or easiest interface to the complicated system. If it wasn't the taxpayers paying for the complexity directly, it would be the government which would charge everyone via those same taxes to implement their own clunky government computer system that people would hate even more.
Countries with simple tax rules don't get to micromanage their economy so much.
The system can be complicated, but all those complications can be handled by the tax agency. For the vast majority of people out there, all the data that you put into your tax return is something that IRS already has, or can easily obtain. And when that is not the case, you should really only need to tell them once (and then update if it ever changes, like the number of kids you have).
Tax filing in US is a huge waste of people's time. I wonder if anyone ever computed the amount of people-hours spent on this malarky, and how much productive output it could generate if used for something else.
Countries with simple tax rules don't get to micromanage their economy so much.