They want you to consume only from them and only what they approve of

Not just that, I remember when app stores were new and people clamoured to be on them AND those app makers would often move to ONLY being on the app store, with anything downloaded off-store being a scam

So a lot of people grew up to use these devices at a time where downloading something off the web was more likely than not to be malware, giving them the ick on the idea as a whole

Fuck, I'm from the time a bit before all of that and even I have a goddamn hard time downloading shit that's available off-store on someone's website out of pure paranoia from those days