Because they have to be contacted to determine a price instead of making pricing clear. (I am not saying that they will not price consistently, I'm just saying it's a bit off-putting)
That's pretty common in enterprise sales. It's a way to have some leverage in implementing pricing gradients. For example, you might want to charge $200k to Microsoft for a given technology, but charge much less to an indie game company since there's no way in hell they could swing $200k for whatever you're selling. Different companies often even want different terms in their contract, so it makes decent sense.