Ok, but why does making the process more painful make people lobby for lower taxes? The connection isn’t obvious to me.

To make this more explicit, presumably the chain of reasoning is as follows:

1. Make tax filing more painful.

2. As a general rule, people will set out to do that which reduces their pain.

3. Therefore, people will set out to do that which makes tax filing less painful.

4. People determine that lobbying for lower taxes will make tax filing less painful.

5. Therefore, people will set out to lobby for lower taxes.

Step 4 doesn't make sense to me because reducing total tax rate and reducing tax code complexity are orthogonal issues, and advocating for lower taxes will not in and of itself lead to a simpler tax code.