Why do agents make so little on average?

[Tyco Bronye]

I understand agents make 20k to 40k per year on average. I'm wondering why exactly this is?

If your a buyer's agent and your client is preapproved to buy a house, it seems like there would be around 100 percent chance of making your 3 percent commission. I can understand there are occasions where your client gets laid off suddenly and therefore can't buy a house, but overall it seems once you've secured a client and they sign a contract with you what else would prevent this sale?

I'm guessing it must be an issue with lack of clients?