This doesn't surprise me at all. Storage is cheap, and it's a lot easier to never delete anything than to devise some system to go and clean up old "useless" information (which at some point you may find useful, e.g. this new Timeline history stuff).

I know often in the stuff I write, instead of deleting data, I toggle a "deleted" column. I always have the option to delete it for real later if I need the storage/clean up the index.