IF both parties of self-dealing grifters acted in concert to do what is best for the nation, WHO is going to stop them, the homeless?

The same people who have stopped every other effort to close loopholes, whether the carried interest loophole or attempts to get rid of the stepped-up basis. Rich people, lobbyists, special interests, and plain old inertia - to say nothing of the many folks who believe it is bad policy to finance the government using these kinds of taxes.

You believe big money owns and controls both parties? Progressive Dems don't really support taxing the superrich?

I believe that both parties have a lot of institutional and other incentives not to aggressively change the tax code to bring in more money by taxing the superrich.

The GOP is obvious - there's huge tranches of that party that are based on hating spending, and part of hating spending is hating taxation.

The Democrats is less obvious, but approximately 61 of the party's 212 House members are from CA and NY. About 30% of the party. Silicon Valley and Wall Street. Those states have huge incentives to keep the billionaire classes happy and stable where they are. Nothing so overt as being "owned or controlled," but also that almost all the individuals who are in positions of power within the party would find it difficult to stand up to concerted opposition of the industries that power their state's GDP. It's the same reason the Democrats don't aggressively take on unions - not that the party is owned or controlled by unions, but that any single individual legislator will find it rough sledding if the unions want to get them out.