Adding to the "no standard bootloader" point: you can't boot your typical smartphone from a DVD or USB stick like you do for a PC. The procedure to flash a new rom is probably meant only for recovery purposes by tech support, rather than the end user
It's mostly not your fault. Apps, games, and socials are intentionally designed to be addictive. That's because the more time you spend on them, the more ad revenue the owners make.
If sheer willpower doesn't work, find other ways around it. Someone else already suggested going to a library or another place, that's good advice. Of you phone is an issue, you could turn it off and allow yourself to turn it back on after you've been productive for an hour, or after you have achieved a specific goal.
I'd keep it on during the shift, and turn it off outside of it. If you don't expect calls or other communications during the shift, put it in airplane mode for maximum savings
A WM crash does not bring down all the other applications... but an X11 server crash definitely does!
In wayland they are the same program (a.k.a. the compositor). User applications can be designed to survive a compositor crash, though many are not able yet
Because you are the product being sold, and advertisers are the customers