1million users waiting even a 1 second longer is about a month of single developers time.
This sort of calculations you preach are inherently untrue, as they completely ignore that 1second times million. After all, nobody bothers economically evaluate just a single second.
But it does account to much, when multiplied by the ammount of users.
And when we multiply again, by the times a single user uses your software, and then again, by the time a users uses different software from other developers who also thought "it's only 1 second, nobody cares", we end up living in world where software usability gets lower and lower despite hardware getting faster and faster.
We end up living in a world where literally weeks are wasted everyday, waiting for slow windows file explorer.
If you'd want to evaluate that honestly, you would probably come to conclusion that microsoft should have a dedicated team, working for decade on nothing but explorer startup optimization, and it would still pay for it self.
But they don't.
Because at the end of the day, this whole "lets evaluate developers time working on given improvement" is just a cope and justification of being us lazy, that only pretends to be an objective argument so we can make ourself feels better