To what end? What are they so sure they’ll find to use against him? So far we’ve learned he paid unusually high tax rates; I expect full disclosure would reveal he paid $0 some years - but only because he paid it years early.
By refusing to release private info, he’s keeping a swath of detractors preoccupied with nothing important. More “power of persuasion”. Should he release the info and satiate their demands, they’d just move on to something else irritating and possibly more harmful.
And between a majority GOP Congress unpersuaded by the sponsors, and the victim/target of the bill of attainder being the final bottleneck to its enactment, there’s zero chance of the bill getting a veto-proof majority.
I never thought before that Trump’s not releasing his taxes to keep Demonrats occupied.