But, the core problem is that in the US we use the tax system as a method for distributing subsidies for various things. Buy a solar panel? Instead of writing you a check, we give you a tax credit. Have a kid? Tax credit.
You could certainly simplify the act of filing taxes, but HR Block and Intuit lobby heavily against that. As far as moving away from using it as a distribution mechanism for subsidies, that complexity could be removed from the tax code but it will get pushed somewhere else instead. I think most people would prefer getting their child tax credit through taxes than having to apply at a welfare office and get a check.