The light time is a fundamental driver here. See more at https://en.m.wikipedia.org/wiki/Interplanetary_Internet
The real issue is the cost, bandwidth and infrastructure in place to make that happen. Scientists would rather want to use bandwidth, power, launch mass and real-estate on the rovers for science instruments - orbiters around Mars which relays data must be upgraded to handle more bandwidth, the DSN on Earth that receives the data can't be dedicated fulltime to one data stream, etc.
(That said, the new laser communication systems NASA is experimenting is pretty awesome, and will greatly improve bandwidth for space missions)