“If wealth was the inevitable result of hard work and enterprise, every woman in Africa would be a millionaire."

Because the world isn't a meritocracy.

Peter is a genius, so he could easily build an app—whether it’s a dating app, a game, or something else—and sell it. It happens all the time in the real world, so why doesn’t he just do that?

The people making millions off "apps" aren't geniuses or even good coders, they're good salesmen with zero ethics, grifters.

Peter has too much ethics to do that. So he can't out onoete someone doing the same thing with no ethical qualms

He did - he owns a very successful company in the comics. 

an 'app' that you use isn't anything more then a shittier version of a website. most 'apps' are not real programs, but instead a portal to a website where they have purposely made the website worse in order to extract data from you by attempting to make you use their 'app'

phone 'apps' are nothing more then predatory garbage most of the time. spiderman has too much good value to be that crooked.