>Why shouldn't Linux be for everybody, usable on every type of device?
It is, but you often have the effort to put into it. Windows isn't usable for everyone, but that doesn't make me elitist, OSX is hard for others, but I don't see that being a problem. Some people can't do everything you do, and there are differences in our abilities. If you expect everything to be easy, and people not willing to put in work to have a functional OS, you should not expect them to use linux, it offers no benefits to most users, its made by hackers to hack on, Android is linux for everyone, and even then they find it hard. Don't expect people to run when they can't crawl.
>Why should we need to rely on proprietary software for our day-to-day tasks?
Because the free stuff sucks, GIMP still sucks. They stuck to having 3 windows open forever, GNOME doesn't like being configured, GTK always breaks stuff, and I just want stuff that "just works". When FOSS does it well like KDE being better than Windows's UI, or Firefox being better than IE6 I will choose it. I don't pick based on their principals, I just want good software, and like most people I am willing to pay for quality. I refuse to use a pinephone out of principal, I refuse to make my life hell.