Because not all Dem senators have the same electorate base whereas republicans (although lately we’re seeing a shift away from this) tend to fall lock step in line. Sinema and Munchin come from very purple states so their seats were never secure. It’s not enough to have a slight majority. Also, the Senate is being held hostage by republicans right now with ever more polarization. I don’t have an answer but to just pin it on the president is asinine. We need to show up to local elections and midterms.