Because its a store/purchase system too, its more comparable to Amazon Prime than Netflix. Prime is also pretty secure as its tied into your whole Amazon account.
Apple TV’s details are peoples whole Apple accounts which is all saved passwords, icloud accounts etc
I do think they should look into separating the two. This would open up more users who just want the TV portion.
Buying a 4K digital movie for 5 bucks, with DVD extras and the possibility you may not have it for life or if you switch countries with your Apple account, is probably worth it. I wouldn’t spent 10 on a digital movie for those reasons, I wait for the sales.
Movies that I really care about, classics, I may save up and buy a physical 4K set.