It is completely legal. A business is not obligated to do business with any one in particular--they are allowed to do business with those who meet their needs or preferences. If a preference is to not work directly with smaller companies but to rather work through an aggregator, that is a legitimate business preference and is not one with which the courts would interefere. (If their refusal to work with you was predicated on something like racial discrimination, that might be actionable; but a simple decision to work through aggregators is not legally objectionable.)Businesses, like people, can decide where to "shop"--just as Dunken Donuts can't take action if you stopped going to them for coffee and instead went to Starbucks, so, too, can you not take action against a client or customer who know wants to work or buy through someone else.