Uber is liquid supply. You never need the same driver and you are usually not in the same place. Uber finds you somebody who can do the gig now.
HomeAdvisor, which is less glamorous but a big business also, gets you a plumber when you need one. Most people need one infrequently so they find one this way. That piece is liquid like Uber right?
But HomeAdvisor, like TaskRabbit, is stuck doing lead generation. They get paid to make the introduction. Because job size varies so wildly and because the relationship goes offline pretty early in the deal (you pay through Uber, you pay your contractor in person usually).
The many to many quality and high frequency of taxis doesn’t seem to work for buildings and maintenance.