It’s not something people like to hear, but the painfully obvious answer is that mainstream Democrats want to lose fights to Republicans, because that is how they get elected.
Elected Democrats could pack the Supreme Court, override the nonsense “debt ceiling”, eliminate the filibuster, pass federal reproductive-rights laws, grant statehood to DC and Puerto Rico, pursue the National Popular Vote Compact (etc., etc…), but they don’t want to do any of those things, or even admit they are possible, because they win more votes from the outrage when Republicans get away with shit.
Without the cover of having the game rigged against them, Democrats would have to contend with the fact that on most actual policy issues, they are well to the right of the people who (have no choice but to) vote for them. Like, most of them would vote against universal healthcare or cutting “defence” spending if they had to choose; but they can appeal to a much wider constituency by avoiding those choices, and letting voters assume GOP obstructionism is the problem.
What’s frustrating about conversations like this one is that progressive voters see each other getting enthused by ideas for change, and just assume that because they all vote D, the Democratic Party must share their enthusiasm. But the evidence says otherwise.
(Though, to give credit where it’s due, Joe Biden did end the Afghanistan occupation, which is 100x more than I ever thought he’d do)
