Why are real estate agent commissions so high in the US?

[Yongming Huang]

I have watched several discussions, including David Greene's video, around the recent lawsuit against NAR and RE brokerages. Learned a lot but there is one thing I just don't understand.

If we look at the numbers, there are 1.3M - 1.5M agents nationwide and there are 5M - 6M transactions each year. So that translates to 3-4 transactions per agent per year. Obviously that's an oversaturated profession. So my question is why doesn't that drive the commissions down? 

I understand that RE agents provide a lot of value to their clients and they have their expenses, etc. But it looks like the plaintiff's attorney asked a legit question: Why the commissions in the US are 2 - 3 times higher than that in other countries? This is baffling to me, too. Can someone help me understand this?