People who don't update you when they say "I'll keep you updated"

I've got a friend who, whenever we plan to hang out will say "I'll keep you updated if we can hang out." And then never proceeds to update me on if they can make it or not. Like, it's fine if they can't, I just want to be told about that instead of being left with no response or update. I get that people can be busy, but at least respond with "sorry I'm quite busy right now so I won't be able to hang out"