It stores file data as calendar events, sort of like that YouTube FS from a while back
This is probably considered abuse under the ToS since you're using more storage than any typical user, and they can't use it for whatever they normally sell customer data for
I seriously doubt this kind of stuff has ever messed with their bottom line. I think they just really resent users trying to do more with their service than they intended.
I think this is a ridiculous sentiment, but I understand why it's so common. Proactively trying to head-off any and all possible problems before they cause measurable impact is not a great way to manage a product.
Maybe they did see impact, but I still would have rewarded non-abusive loyal customers for using the product—maybe restrict access based on resource-usage rather than hitting people with TOS violations. Instead this attitude (plus their generally very poor track record at supporting and improving their own products) has caused me to abandon all google products outside of work.