Why do so many shared subscriptions work fine at first… then suddenly stop?

So I've been rotating through different shared setups for Netflix, Spotify, some AI tools basically whatever I can split to save money and I've noticed this weird pattern that keeps happening where months 1-3 everything's perfect with no issues and full access feeling like I hacked the system, then month 4-6 I start getting small hiccups like getting logged out once or a feature stops working for a day, and by month 7+ it either dies completely or I'm suddenly locked out with zero warning. I've gone through three different setups now and it's literally the same story every time which is annoying because they all start so stable that I keep thinking maybe this one will be different but nope, always ends the same way.

Is this just my terrible luck or is there something structural about how these shared things work? Do platforms intentionally let them run before clamping down or is it more about whoever's managing the main account eventually changing something? Anyone else tracked this pattern or found setups that actually stayed stable long term and what was different about those?