Sure, the majority of mobile apps suck. But even then, 1% of it is still orders of magnitude larger than the number of "Linux" apps, and there are surely more actually decent mobile apps than that.

Besides, open-source doesn't have to be GNU, there are a bunch of open source apps on F-Droid.

I also reject non-free apps whose main purpose is to snoop on their users like Facebook. But what about dozens of FOSS projects like Home Assistant, Jellyfin, Nextcloud, KeePass and many others? All of these have polished clients that work perfectly on Android and provide an experience that rivals or surpasses commercial offerings. They took years to develop and I don't expect Linux phone versions will ever be released because of the chicken and egg problem. You can emulate these apps with Waydroid on a Linux device, but you will almost certainly lose some features like GPS access or notifications. At the end of the day, you will mainly be running Android apps anyway, free or non-free, so you are better off with an Android device in the first place.