I've been a professional software developer for over 10 years. Long enough to see the shift.
I didn't say that it didn't happen. Just that it's not the norm. If you think it's the norm you may be a bit out of touch.
I'm well aware of the fees that Square charges. I've built a multitude of sites that use it. 2.9% + $.30 is far less than 30%.
Been a professional software developer for over 25 years with products in the Apple Store. I deal a lot with resellers like Best Buy, OWC and many more (such as Computer City, CompUSA and others over the years). 30% is a good deal compared to what developers are use to. My pricing comparison was to resellers, not your own website processing fees.
If you don't like it, there is no one holding a gun to your head and making you put your software in the App Store. You can simply sell elsewhere. Developers choose to be on the App Store because it means tons of additional traffic and lots of additional revenue.
You may get 10 extra buyers on your website by not putting it on the App Store, but you're losing out on 10,000 extra buyers that would have found it on the App Store. Which one you want is all your own choice.
Charge to process a payment and cut to sell your product for you as resellers do, are two totally different things, which you seem to be having problems separating. The App Store is doing FAR more than simply processing a payment.