My main problem with the current crop of Linux phones is, or at least it's my impression - is that they still struggle with the basic phone part. As in network connectivity (at least in the US), making and receiving calls, SMS & MMS, and VoLTE support. If there's a Linux phone where that stuff is solid and works, I'd buy one. I don't really care about the whole app ecosystem - I barely have any apps on my Android phone now.

Most Android apps can be run under a mini-VM in the Linux systems I've tried - but some apps won't function well that way (banking, NFC tickets, etc)

Waydroid works really well to run Android apps on mobile Linux, even for games. Doesn't help for banking apps though as they'll usually lock you out due to not passing Google safety checks.

I think I'd be willing to let go of the handful of things that are exclusive, given that I could probably do more with a proper Linux system. It's the basic phone functionality (as others have mentioned) that keeps me from switching.

Wait, Linux phones are a thing? How do they get the market share to compete with the big tech?

I thought so too, but over the years I have migrated so much of my life away from apps in order to see if it's possible and apart from games I find that with a browser and an email client I don't really need apps. Still use apps though, they are way more convenient.

Banking is tedious without apps, but works with browser and an MFA-dongle in my country.