A big part of the current "OBBB" in the Senate of course is extension of the "Trump tax cuts" from 2018. Those tax cuts are actually pretty minor for folks with higher incomes, the dollar amount looks large but it's not really enough to impact one's lifestyle that much, for some couple earning say $400,000 a year. The tax cut for a couple earning $50,000 a year is of course much less in dollar amounts but could be the "edge" they need to stay afloat. So, some of it is clearly in the interest of folks earning lesser amounts of money.
Biden was President recently of course (in theory) and didn't put much effort into increasing taxes.
FWIW, I dislike many portions of the bill, I think trying to cram "everything" into one bill is a mistake. The work requirements for Medicaid at least sound like a good idea to me, but I don't know enough about that to have a hard opinion. Previous Democratic Presidents have supported similar work requirements.