The iOS reminders app already has a concept of "remind user <x> at <y> time" so Siri is just creating one of those.

The bedroom light may not have such a structured concept already existing (or may not expose the full-featured API to Siri).

If it can turn lights on and off, and separately play some sort of reminder sound after five minutes, then it can turn the lights off after five minutes.

It just pipes the command to the appropriate app/service. That's why it doesn't work. Reminder service supports that, but lights service doesn't.

There is no "general ai" doing stuff in the background.

The lights service doesn't have to know anything about the reminder service.

The reminder service needs "one line of code (tm)" to go "After five minutes, send <this> to the lights service".

The problem is that there are so many different permutations of this that the reminder service (and every other service) would then need to accomodate for hundreds of other scenarios, such as:

- When I arrive at home, turn on the lights - After five minutes, play this song - Lock the front door at 10pm

And then the reminders service (which is a to-do app!) suddenly becomes 100x more complicated than it was to accoomodate all these strange use-cases that are outside of it's bounded context.

It's easy to implement a single use case, it's practically impossible to manually code every possible use case (which would also probably create a huge amount of tech debt).

Google assistant/home supports it. Just tried it.