Not only that but the technology they use is mostly still from the 90s. RETS is the closest to a standard in the industry but its a clumsy XML based schema mainly consumed by WordPress / PHP sites.
2. The amount of money involved in a real estate transaction encourages prudence and due diligence.
3. Every piece of real-estate is unique. That means that acquisition always entails tradeoffs and opportunity costs.
4. The real-estate sales market has aspects of a highly competitive commodities market. This means that ultimately, technologies that improve efficiency ultimately result in lower prices across the industry. For example the internet has tended to lower real estate commissions as sellers are more able to market properties themselves and to are better able to negotiate with multiple agencies.
To put it another way, what's the business case?
The amount of money involved is exactly why I would expect there to be good tools. If a better website or improved communications can make the difference on a transaction worth thousands would that not encourage higher quality tools?
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.
You are right that getting listings is the primary pain point but I would have thought standards about how properties are categorised etc would help with this. In particular as real estate becomes more international it would really help for a broker in Mexico to be able to send details of a property to someone in Russia in a format that can be mutually understood.
I can also imagine a demand for open source tools that can help in the communication between all the different parties to the transaction. I have ideas about how such a tool could monetise and I'm surprised that no one else has thought to do it.
A quick google for "real estate open source" shows mainly outdated projects, several of which are not actually open source.