I use Chrome 99% of the time. But I have it configured and hardened to the point where a few websites with tons of trackers no longer work. I fire up Firefox if I need to log into corporate sites that don't log in on Chrome because too many redirects or strange third party cookies for example. I also use Firefox if a site is unencrypted. I have to go through too many steps to whitelist a HTTP site on Chrome lol. It's faster to quickly glance in Firefox and then leave. But sometimes that's not enough. I use Tor browser because the tweaks I made in Chrome and Firefox improve security but at the price of having a unique browser fingerprint. I also want to access sites that I find interesting without worrying if something is tracking me.
The main reason is, a sense of freedom of choice. Chrome OS can feel claustrophobic when you are locked into Google's ecosystem after a while. Firefox, Tor open a window. Many of the apps in the screenshot were installed through terminal for Linux or sideloaded via adb because Google lied that they were not compatible when they are.