AFAIK someone is working on it. But the problem is the high dynamics of public transport. Routes and schedules get changed quite often, schedules might be quite irregular (think only Sunday at 3:14). And all that data has to be stored offline. Stops might be changed do to construction work for a week. And that is in the optimal case: In some countries the bus comes when it comes, and stops if it wants to stop.

Currently you can see where the lines of a bus or the metro go, but that's about it, I think.