Adding certificates is a 5 step process: Settings -> Privacy and Security -> View Certificates -> Import -> Select file and confirm. That’s on firefox at least, idk about chrome, but probably not significantly more complex. With screenshots, a small guide would be fairly easy to follow.

Don’t get me wrong, I do get your point, but I don’t feel like making users add client certs to their browser storage is more work than helping them every 2 weeks because they forgot their password or shit like that lol. At least, that’s my experience. And the cool thing about client certs is they can’t really break it, unlike passwords which they can forget, or change them because they forgot, just to then forget they changed it. Once it runs, it runs.