I thought they were going to roll out an Apple app to other devices like the Roku etc. ...
... yep "in the future"
"Apple TV+ will also be available on the Apple TV app on select 2018, 2019 and newer Samsung smart TVs, and on Amazon Fire TV, LG, Roku, Sony and VIZIO platforms in the future."
Without 3rd part hardware support they'll really limit their reach.
None of Apple's content interests me though, even for the price.
Still plenty on Netflix keeping me entertained, and Disney has some content I'll want if they ever get their app/subscription released in the UK so I'm more likely to spend my money on that.