I used to ask the same question myself. I went and talked to many real estate agency principals and found that the most important step for them is to get listings. If you don't get enough listings, then you don't have sufficient cashflow.

Buyers do look at the real estate web sites to find properties that meet their needs, then they go and inspect them, etc. The transaction involves contracts, lawyers, conveyancers, title registrations, etc.

So when you talk about disruption, which portion of the chain are you talking about? An end-to-end system would need to hook into many existing systems and those are different for every country, state, county, some times even cities.