What programs are you using in such a fashion that simply having the program autostart at boot is not feasible?

I used to have a nasty habit of opening a text editor during the day and taking random notes during phone calls or as I worked. Several forced restarts (administrative, accidental or hardware related) forced me to start using those sticky-note apps. I've moved to Joplin now (very structured, supports markdown, syncs to dropbox periodically, is multiplatform)

The browser thing resonates though. It's not just which websites are open, but what state they're in (ie: logged in, midway through filling out a long form or survey). In a pinch I'll just 'kill -9 firefox' so after the reboot it automatically restores tabs and windows, but it's still messy. Sites that require authentication will just bounce you to the login page and may not "remember" where you were trying to get to. Maybe we need hibernate for browsers.

I could understand if you're away from a plug and/or on the move though.

Also if cars have computers, don't they cold boot when you turn the car on? Phones and smart watches never truly "turn off" their screen goes into sleep mode which is fast to turn on

Because it’s way more convenient. Next time you go to open your front door, take out your phone, start a timer for 30s, and then put the key in the door once the timer expires. Once you’re used to something being near-instant, there is no going back. Waiting is frustrating.

Personally I haven’t used hibernate in over a decade and my machines typically run 6 months until I have to reboot for updates. If I had to wait ~10 seconds every time I wanted to google something, I wouldn’t use my PC nearly as often as I do today. Maybe that’s why mobile is dominant in so many categories like web search.