Most developer focuses on app coding. To create a server to talk to mta is a taxing work. It does not pay for serving only one app.
Create a bus time server that talk to mta. Open it to all developers. Only charge developers who exceed certain volume. It will reduce the users. Or use it to brand itself.
Unlimited Internet. And cheap computing power. Helps these developers.
But is it fast enough?
Get gtfs data. Put in database. Answer queries.
Provide schedule and live data. Provide notification.