They shouldn't but they do. Making the world a better place is not what founders have in mind. What they have in mind is "we are looking for an exit and retire young", for nearly all of them. Unfortunately those words are not something they can write in a mission statement so they must be creative.

Not just startups, this cognitive dissonance is everywhere in business and we're supposed to just swallow it. Honestly I've been a cynical prick for most of my adult life and for a while I played along with it but it just does not align with my values and keeping up the pretense is draining.

I mean uh. Come work for us / hire us, we're the best at what we do! Honest! AI!

Silicon Valley made fun of it: https://www.youtube.com/watch?v=B8C5sjjhsso

Unrealistic goals seem to be a core tenet of capitalist realism. You see the same thing in politics: Trump is going to stop the Ukraine war in one day, Musk is going to cut 2 trillion from the US budget with efficiency improvements, etc... . A couple of years ago my company gave OKRs a go. One of the principles is that objectives should be practically impossible to reach, i.e. if you hit 100% of an objective then it wasn't ambitious enough. It's a surefire way to ramp up anxiety and stress on a team.