As long as it's possible to do this and there aren't serious high-level repercussions for it, it will keep happening. This is why people flock to e2e systems, because we don't trust corporations or governments to protect us.
Edit: Removed Signal as an example.
I don't know about the others but I don't think Signal does this. Signal offers the user the ability to backup their messages, and lets them password protect them, but the way you've written this implies Signal is uploading messages to Google of its own volition, unencrypted, which afaik is not the case.
FTFY. The only solution is for the information never to exist in the first place, never centralized, never even collected.