For desktop usage, I would be absolutely shocked if ext4 isn't the most common filesystem by a pretty wide margin. Its the default on Ubuntu, Debian, and Mint. Those are the 3 leading desktop distros.
No one is going to write a blog post titled "Why I just used the default filesystem in the installer" but that is what most people do. Things like btrfs and zfs are useful, complicated technologies that are fun to write about, fun to read about, and fun to experiment with. I'd be careful about assuming that leads to more general use, though. Its a lot like Guix and NixOS, in fact. They get all the attention in a forum like this. Ubuntu is what gets all the people, though.
No one is going to write a blog post titled "Why I just used the default filesystem in the installer" but that is what most people do. Things like btrfs and zfs are useful, complicated technologies that are fun to write about, fun to read about, and fun to experiment with. I'd be careful about assuming that leads to more general use, though. Its a lot like Guix and NixOS, in fact. They get all the attention in a forum like this. Ubuntu is what gets all the people, though.