I assume these design decisions are all driven by teams juicing business metrics, at the expense of usability. Need to increase the “number of streams initiated” KPI? Trick people into resuming videos they already watched 99% of. The alternative, that teams simply don’t care or know how to design good user experiences, is too depressing.
Another example: both Netflix and Amazon make finding your saved watchlist difficult probably because they want you to watch random other content instead of watching your finite watchlist (and then unsubscribing when you finish everything on your watchlist).