I imagine it would be relatively easy for them to operate as actual brokers also. I wonder what has stopped them.

That's the thing... it's not as easy as you'd think. There are a lot of barriers put up to protect the industry. In many ways, innovation should have put Realtor's out of business like they did Travel Agents. The difference, Travel Agents didn't have a powerful lobby group like NAR.

Question: the internet has been a boon for shaking up entrenched incumbents. What happens when the internet gentrifies? Will we have even more hideous incumbents with no new tech on the horizon to generate a disruption event?

Brokers are subject to regulation which limits what they can do. For instance, they can't receive kickbacks from mortgage providers