Why is Google Keep's use of background data suddenly through the roof?
Well that would be a data leaking app as per April 8th. And I never saw that coming because I have a large amount of data package for myself but would go and check.

This is a hell lot of data being used up by such a tiny app. I mean in my phone 200mb+ data is either used up by Google Play store or a Browser app by which I downloaded files (audio, video, images etc). Otherwise I never saw such event.

However, if you want to contact Google about it. They would be waiting for the feedback and you can include this as the feedback message. But if you want them to get you some data package (maybe I got confused and mis understood your point of view for contact) then they won't do it.