That's not an exaggeration for comic effect. There's literally 50 bits per second from each satellite. 6.25 bytes.
So the navigation messages are packed extremely densely. To the point that plenty of numbers don't even start on byte boundaries.
GPS relies on receiving extremely weak signals, often with a very limited receive antenna. This means there's a real trade off- you can send a limited amount of data over a given communication channel. Increasing the data rate might require increasing the transmit power / antenna gain of the GPS satellites, or requiring bigger / better receive antennas on GPS receivers.
Here are the parameters involved: https://en.wikipedia.org/wiki/Shannon%E2%80%93Hartley_theore...