Largely because Trump did a lot of waving around of the Executive Order wand.
Problem is, that only works when you have flunkies that can back it up for you. Trump had a horde of goons that were eager to drink the kool-aid and support anything he said, reasonable or not. Biden is working with the opposite, with a congress full of people that will reject anything he says even if it's a genuinely good idea. Obama struggled with similar problems, being stonewalled by congress.
The Republican party long ago abandoned any pretense of actually governing and has simply become anti-democratic. This, in part, though not completely, is what has halted Biden's progress, just one in a line of many of his forebears and probably several of his successors unless America collectively pulls its head out of its ass.