If somebody is renting points as a business, there may very well be a tax depending on where they are doing business. This law actually applies even to personal transactions, but most people don't realize that or follow through on the tax obligation and the government has almost no way to know of the transaction or prove it so they don't pursue it either.
Renting points is a business transaction (you are apying money for a good or service) and the transaction is subject to sales and use taxes (depending on state and local laws). Just because many do not submit tax in the performance of this type of transaction, does not mean ignoring it is legal or correct.