I prefer to keep stuff separated/"compartmentalized". And thus far, I have Hulu, Disney+, Paramount Plus, Amazon Prime, and Curiosity Stream (will add Apple TV+ soon, but the former 2 I've long stopped the subscription). I also have YouTube, but no subs there. At most, I've did a few one-off purchases to rent some films, and purchase seasons/single episodes from TV shows.
In addition to having one place for your billing, I'm assuming if you order a service through some other (for example, PP through AP), then you would use the interface of "the other" (Amazon Prime in this case). Another would be certain restrictions. For example, I read in a Reddit thread that if you want to us Hulu gift cards to pay for Hulu, you can't do that through the iOS App Store (or however it's done through Apple).
Curious, are you watching through an app, or a browser? I only do the latter, but I'd imagine some may prefer one or the other.