Its a double edged sword. Do you think the people of say Atlanta want all their judges appointed for them by the party that controls Georgia legislature?
Of course you don't want the legislative or executive branch to appoint members of the judicial branch. All three branches are supposed to be strictly separate from each other.
If you did allow the other branches to appoint judges, the bench would obviously become stuffed based on who's currently in power.
Often the Party and the electorate have differing goals. As a general rule the Republican Party didn't particularly like Trump, but the Republican electorate adores him. Likewise the Democratic Party really likes Biden, but my general feeling from Democratic voter was, "we'd rather Bernie or Yang, but have have to dump Trump."
