It's a lot of trouble and ultimately they lose money on the changes. Right now if someone goes over whatever limit they set for themselves they mostly pay the chargers or on the rare cases they try to dispute them. With a set limits the provider will always lose business. Also trying to make sure the limits are not met is extra CPU power that could otherwise be sold for a profit. Bottom line, it does not make business sense .
It doesn't even make sense as a competitive advantage since it costs more to maintain than what it brings in. If I owned the cloud service I would only set the capability if the customers demanded it to the point of them switching to a competitor en masse.