Hardware compatibility. I have one machine that won't boot any Linux installer at all. Another with constant gpu driver problems. Another where Bluetooth doesn't work at all. Another where wifi firmware crashes all the time. It never ends.
I use it every day across many machines. Still continue to have serious hardware compatibility problems with a wide range of devices. It's extremely frustrating.
I realize not everyone's experience is the same, but it can still be a really bad time for some people. Maybe the same can be said about Windows too but I still think it's not as bad.
If you try to get a professional Photoshop or After Effects or Resolve or Solidworks or Quickbooks etc etc. user to use a FOSS equivalent you will be laughed out of the building.
It's not that they won't learn, it's that the alternatives literally can't do so much of what people need it to do. And at the same time they most often look worse, are harder to use, and are sometimes less stable.
A prime example myself, I have tried to use kdenlive for YEARS to do simple subtitling. Every few years I try the latest version. Without fail it ALWAYS crashes within 20 minutes.
Same for Audacity. 5 minutes into clipping some audio... crash. 3 times in a row. And it looks dog ugly enough to turn me off to even wanting to try it in the first place.
Or GIMP, it can't do non-destructive editing, this makes it completely unusable for many professionals.
It's not just one or two things here or there in these apps, it's huge sweeping problems across the entire FOSS landscape, almost none of the options are comparable for professional users.
would certainly love to see your side by side comparison of a large difference in memory usage between the two using the same tabs and no extensions with up to date versions.