rich donors want it complex so they can keep finding the loop holes that let them pay nothing most years.

Which is not a solution because just because while you pay less taxes you still have to go through the process

Which is why they keep wanting to defund the IRS (example):

1. It allows the wealthy to cheat on their taxes with less concerns of getting audited or if they do get audited, they can outspend the auditors.
2. It would have de-funded this measure the IRS is getting ready to test which would allow Americans to figure out and pay their taxes without feeling compelled to go through middle men like Intuit and TurboTax.

Edit: More direct example of point 2

https://www.opensecrets.org/news/2023/09/tax-prep-companies-lobbying-against-free-file-face-scrutiny-from-lawmakers/

After President Joe Biden’s December 2021 Executive Order instructed Treasury Secretary Janet Yellen to consider “expanded electronic filing options,” Yellen testified before the Senate Finance Committee that building a free direct filing service is “definitely a priority.” The Inflation Reduction Act of 2022 allotted $15 million for the IRS to explore the creation of a free federal tax filing service.

In May, the IRS released a report announcing plans to launch the pilot program for the 2024 tax filing season and indicating that most U.S. taxpayers are interested in filing their taxes directly to the IRS for free.

But in June, Republicans on the House Appropriations Committee proposed a budget rider that would bar the IRS from using federal government funds to create a government-run tax preparation software, unless approved by the House and Senate’s appropriations committees.

They aren't the only one, but they are the largest one. They didn't make the system the way it is, but they benefit massively from it staying this way.