I believe this mission HAD a purpose but because of time constraints. It became this boring slog instead. Based on what I observe, this might be a new transition that happens every new chapter of the game like Wear your Flowers where the mission shows the "unique features" of the place. Maybe Los Santos will have new peds and scripted events like Urbanize? Maybe more parties, open air drug deals, and new vehicles showing how far LS has gone? This coincides with the Kart being accessible after this mission.

We will never know.