Because, frustratingly, Biden isn't the sort of LBJ-esque power player who can haul miserable DINOs like Joe Manchin and Kyrsten Sinema into the Oval Office to threaten them with political death unless they fall into line with his agenda. The fact of the matter is that just like in Obama's first term, Democrats really only had control of Congress for two years, and by a margin so slim that they needed unanimity to actually advance rules changes in the Senate, let alone legislation. That meant that Biden's entire agenda was bottlenecked by two of the most worthless assholes in the whole party, people who are definitely guilty of the short-sighted political gamesmanship that you want to ascribe to the entire party. Their obstructionism meant that, because of Senate rules, there's only one chance or year to pass major legislation, and even then it has to ostensibly be budget-related.

Despite all that, Biden and the rest of the Democrats did manage to get major legislation on climate enacted, in the form of the Inflation Reduction Act. Was it the whole Green New Deal? No, Manchin the coal baron wasn't going to vote for that. But it's still major change in a positive direction. Your frustration that there hasn't been more is misdirected at the party generally, when it should be aimed at two senators in particular -- and the solution to that is not to throw up your hands and declare "both sides are the same!" It's to get out the vote for more progressive legislators to make those assholes politically irrelevant.