WTH is the Apple Watch still so limited?

Well, a few things:

Due to the fact that Apple Watch functionality is limited to the configured iOS actions, the current Apple Watch functionalities are very limited.
If you look at what other Watch Apps are capable of, it’s a shame that the HA app is just a basic list of actions with a configurable icon, color, etc.
I’m talking about graphs, data, different subwindows, etc. Take a look at the Sleep app for reference.