Adobe is very good at building software. It's not the problem. It's not that Adobe can't compete with Figma. It's that they don't want to.
Adobe has a great engineering team and ships wonderful products. The problem with Adobe is that the business side is anticompetitive, exploitative, and sleazy. Buying Figma, they lose a competitor. Competitors have a nasty tendency to expand to adjacent markets, and that's the sort of thing Adobe likes to nip as early as possible.
If not for their business practices, I would totally buy Adobe products, because they're great.
As is, I don't know if Adobe won't triple prices tomorrow for me to continue to be able to edit my own documents (once they know I'm locked in), or find some other way to !@#$ me up the !@#$. The slight hit to product quality going to competing products and open-source is more than made up for with the stability of having a reliable business partner, or source code I can build myself, respectively.