Editorial speculation. Radio plays heavily into the GTA vibe and is intentionally region-coded.
Likely musical territories
Latin / reggaeton down Little Havana way. Hip-hop / Miami bass sound near the coast. Synth-pop / 80s-referencing up on the strip (a callback). Country out in the rural towns. House and EDM for the nightlife.
Every Rockstar GTA has had region-coded radio. GTA 6 will have it too.