They do it because they can, and because they can get away with it.  Anything can be a TOU Violation when one reads the rules, and WHO deletes is more the issue than WHAT, IMO.  Many are Admin/non-reviewable, for the express purpose of suppressing differing opinions, TOU's aside.  Can't drive the car if you don't have the keys.

In reality, if the Company would give us what we're all waiting for, there would be fewer deletions/debates, unless it was to pick it apart.  No doubt that would/will happen, either.  JMHO.