no matter how much money i would make, you will never see me flying first / business class before i'm 40

you can use the funds in like 1000 more productive ways than buying comfort for a few hours

a cost of one first class flight can buy you a year of workouts with a personal trainer which will delay the necessity for sitting in the first class for another 5 years

pure destruction of capital

most people aren’t spending money, but utilizing points or upgrades when they fly business or first class, also, there are times where you may pushing things to the limit and lay flat is the only way to have any chance of sleep on a red eye, while I agree with you in principle, in practice there is a lot do nuance to flight upgrades