Per the 800-lb gorilla itself:
At Google one of our key philosophies is to take risks and to experiment. To that end, in July 2009 we announced the ability to find property for sale or rent directly on Google Maps. This is one of the “search options” next to the search box on Google Maps, and is currently available in the US, Australia, New Zealand, the UK and Japan.
The search giant (I think we’re required by law to refer to Google as “the search giant”) cited low usage and “the proliferation of excellent property-search tools on real estate websites” as major reasons for the decision.