(sorry for the long answer)

Besides the vendor-lock-in and "enshitification" things (which are also a direct consequence of capitalism) just compare the Microsoft Office Suite against LibreOffice. It's not even close.

Don't get me wrong it works good enough for typical use-cases but the difference in depth, quality and polish is huge. Same with Photoshop vs Gimp, After Effects and other Adobe stuff.

Tons of software doesn't even have proper Open Source equivalents because they are so nieche (compared to office software or VLC for example).

Unity (vs Godot), IDA Pro (vs Ghidra), EnCase, SolidWorks, etc.

Check out how Mozilla Firefox makes its money. They are over 80% funded by Google and make all kinds of shitty decision. Not because they are bad people but somebody has to pay development because good software doesn't just happen because a hand full of junior devs have some free time.

Look at the shitty Ubuntu decisions, also done because somebody needs to pay for development.

Look at audacity, redis, FluentAssertions, OpenOffice, MongoDB, ElasticSearch, MySql, IdentityServer4 and many more OpenSource projects that went commercial or changed their license because it was unsustainable.

You can of course always fork, but the forked project than has the same issues. Development works as long there are skilled people motivated to practically donate their free time in exchange for nothing. That already greatly limits the people that even can work on open source and if their situation changes history repeats.

It's not even OpenSource only. Look at YouTube creators especially science educators. A lot of them with great content and talent explaining various topics. But also trying to sell you stuff like squarespace, Brilliant and NordVPN because it would be unsustainable otherwise.

So yes great (by that I mean big polished good quality "unenshitified") FOSS won't happen under capitalism because writing software is time-consuming.

Why do you think people pirate commercial software like AutoCAD, Photoshop, Lightroom, InDesign, MS Office, SketchUp, SolidWorks, etc.? Because they are polished in a way no open source project could be, because hundreds of engineers worked for decades on those.

All that said, FOSS is great. I use and rely on a tons of OpenSource software, self-host a lot of services, regularly contribute to quite a few projects and also am the maintainer of some libraries other people use (even commercially) and I still stand by what I wrote before:

Open Source can't be as polished and high quality as big commercial software because it doesn't have the funds to do that. Five motivated people are not enough to write an After Effects competitor.