I imagine you suffer from market size problems.
This works when one destination has strong mass transit connections (e.g. the casual carpooling over the SF Bay Bridge), but without that, pairing seems hard.
If I'm going from X to Y, what are the odds that there will be another person traveling along this route that within the next M minutes will be near X? Note that M must be small to encourage me not to use alternative options.
If there's not enough drivers, passengers stop using it. Not enough passengers.. drivers stop using it. Because of the need for both source and destination alignment, unlike the taxi which just needs source alignment, much larger critical mass is needed for this to be useful.