AIUI, the amounts spent on lobbying are large of you compare them to what ordinary people spend on rent, but piddly if you compare them to what a government collects from even minor taxes.
Meaning they have a lot of taxable assets, under current tax code. Otherwise they wouldn't care. There are estimates that every dollar spent on the IRS yields 6 dollars in collected taxes [1][2], without passing any changes. The only reason to lobby against the IRS is to avoid paying the taxes you already owe.
