Because there's massive marketing spend to make everyone feel like subscription services are the only option. Because all the investment in development is only in efforts with rent seeking subscription crap.

We could have easy plug and play local interaction or for remote operation, a self hosting platform. Instead you generally have to carefully research until you find some brand that is amenable, maybe flash over their firmware with a custom image, and put the pieces together yourself in something like homeassisstant. There's nothing preventing companies from making local management as easy as cloud management except the rent seeking.