It seems like proprietary software has a big advantage when there's still lots of room for improvement, so that investment in further development pays off.
However, in some cases, there's little room for real improvement, and the thing becomes a "solved problem" for the most part. At this point, the proprietary companies then start enshittifying the software (look at Photoshop, now a cloud-based program) to try to extract more money from users, and to keep users on the upgrade treadmill. Part of this is probably from the way corporate politics work: when you're a manager with a team in place, you need something to keep that team busy, to justify your team's continued employment to upper management, so when you run out of useful improvements to make, you invent less-than-useful "improvements" (e.g., ugly new UIs).
This is where FOSS seems to be able to do well: it doesn't need to waste resources on useless improvements (we'll ignore GNOME for a moment as an exception), and can just focus on delivering the necessary functionality. Once that's done, it can just go into maintenance mode and people can move on to other projects. Until then, it can continue to improve and attract users to switch from the enshittifying proprietary stuff.