AWS sends out targeted notifications via email and via alerts in the console if you are a current customer of a service that is changing somehow. It’s pretty normal that they don’t send out a press release and blog post every time something changes - if they did it would be a mass overload of such releases.

You, hopefully. I mean if you're an individual then I can see it but at work we do a monthly billing review to catch things like this. I hope you're not treating AWS entirely like a black box money pit and actually look to see where it goes.