This isn't a technology problem, it is a geometry problem. Car pooling/sharing cannot work very well because eventually the car needs to go down some "dead end" that you didn't want to go down to pick up/drop off somebody, and that time is wasted. If you are the last one on and first one off it is great, for everybody else it is wasted time where they are not making any progress getting to their destination. Everybody would be better off (less congestion - less expensive roads need to be built) if everybody carpools, but you are always personally better off to be the one person who doesn't.

It may seem like you can solve this by just picking up in the neighborhood. However there are not enough people in any given neighborhood to make that work. This morning exactly one person (car) passed me on my way to the bus stop - I don't know if this person would go the same direction as me or not: there isn't much opportunity for ride sharing within one neighborhood.

Transit has the same problems. It solves them by forcing people to walk to the stop/station. At least everybody feels like they are making progress. They also come on a schedule which means you can't leave when you want to.