Notifications, as an active research area, just hasn't developed yet. It's mostly because the concept is very new. But expect much more research and much smarter commercial systems in the next few years. I won't be surprised if notifications become our primary mode of interaction with the digital world.

Also, the training data easily goes into thousands or even millions of samples for even modestly used applications. Unless you mean train a different model per user, in which case, yeah, it won't work.