Right because the alternative has worked real well - letting any random app on the store. I specifically don’t download any random crap on my computer but I do on my iOS devices. You can’t even trust known companies like DropBox and Zoom. They have both done shady things on the Mac.
I’m sure you also think that physical good stores should bare all of the cost and allow companies to sell things for free without a markup...
Well we can talk theory or we can hobby history. How well has the open ecosystem on computers worked for the average consumer? Viruses, malware, ransomware, adware dozens of toolbars on their browser, programs randomly uploading their contacts, etc.
I know plenty of people who won’t download random apps on their computer but will on their mobile devices. Because they have had bad experiences before.