I think that technically the seller's agent is the one given that 6%, but then they split it with the buyer's agent 50/50.

The argument I've seen made is that the buyer's agent's motivation to lower the price comes from wanting their client to actually make the purchase. That said, I'd think that this is only motivating them to get down to the highest price that the buyer will accept paying, rather than the actual lowest price that's theoretically possible.