Blue, there is another option. I would say that mass growth of whm might include the fact that they also specialize in free hosting, which, no science testing necessary, attract masses of webmasters. If they are later on "switched" to or advertised to of whm paid services, even though they are not using all of the 50 GB, then might make a profit. However, advertising more resources for sale than a host can provide in full is misleading advertising.

They might also receive extra revenue from advertising off free account holders. Of course these are all guesses.

Best,