These are weird questions.

Who stands to benefit financially?

The developer, if they are distributing themselves. Also potentially no one. That shouldn’t really be a concern though, why are you concerned with what seems to amount to “someone needs to be making money off me, I want it to be Apple!”

Who are the stakeholders?

Again, literally anyone or no one.

Why can webapps not be used instead?

Why can’t you use a web app for all your PC applications? Because native APis are always going to be more expansive than what is made available to a web UI.

Do side loaded apps have access to apples APIs, do webapps not?

It’s a mixed bag. Some yes, some no. But you’re generally going to be able to do more with native apps than a web app.

Can apple, like Reddit charge for use of said APIs?

Why… would you charge for local API access? You’re paying for the hardware, you’re paying for the computation time, you’re paying for the electricity, why would Apple get paid?

Also, why does everyone seem to portray such a personal stance on the subject, how would allowing side apps benefit any of those who have downvoted me in their day to day lives.

Apple explicitly doesn’t allow certain kinds of apps on the App Store. Many of those can be replicated in a web app, but not all. One easy example is game emulation. You can do some emulation in a web app, but the performance isn’t going to be great. You can sideload an app that does it better, and you can actually force load with a different flag to have them work even better than that. One such emulator is Delta.

I’m a little concerned on your line of questioning honestly. It seems like you’re extremely concerned that the (first or second depending on the day) largest company in the world is going to lose out on a little money. Why are you so invested in them making money? How does Apple making more money benefit you in your day to day life?