The catch is is that it increases your spending. If we take PS4 attach rates as a realistic estimate (I think the XBOXs are a bit lower), consumers buy on average, 2-3 games per year, and those games aren't consistently at full cost.
Gamepass has you paying $10 a month, $120 per year, to play a what is realistically, only a small selection of games on the service. While the sum total of the games in the service offers obvious value, it's additional to the average spend. Further, the games on game pass don't even necessarily overlap with the games that those people would be buying, as many titles from third parties don't hit the service, at least not around their launch window.
So as a result, I suspect for the lay consumer it often increases their household spend, without necessarily seeing them engage with much more content on their system.
I know that's been the case for me and my partner. I like having game pass ultimate, and I downloaded maybe 30 games with good intentions to play them, but I've actually only played Sunset Overdrive, Forza Horizon 4, Halo Anniversary Ori 2 and Crack Down 3. I would have never bought Crack Down 3, and frankly I didn't enjoy the time I spent with it. My girlfriend enjoyed Ori though I haven't played it, I like Forza Horizon 4 a lot, and I've also been enjoying Halo Anniversary. So that's a sum total of two or three games that I can say we would have paid for.
The big caveat on top of that, is that with gamepass I don't even own those games.
It's the same with Playstation Now. I have a Playstation Now subscription and frankly, despite criticism I think it offers just about as much value as game pass. I recently downloaded WRC8 from there and I've been enjoying that, as an example. But it's rare that I really engage with content here. I browse and download games here and there, in my head I appreciate the variety, the idea that these services will help me keep myself entertained when I don't know what to play, but at the end of the day, I don't think I get a tonne of value from them. Especially when compared to buying games in sales, or buying used games.
It's all just about increasing household spend at the end of the day, and the up front value of these services (both game pass and PS Now) is technically, rather astonishing, but it's encouraging spending that I wouldn't have otherwise undertaken, and at the end of it, it leaves me with nothing to show for it.
Writing this all down makes me think I should just cancel my subscriptions and buy the games that I really enjoy on these services... but the idea of shelling out £100, that's a hard pill to swallow compared to letting them roll over for another month... or another year... and in my mind, I think... what if they add something I want to play next month? At the end of the day it's not a lot of money so it's easy to let it slide, but I think these types of services don't truly offer good value for the average consumer.