Why is GTA 5's Los Santos on an island?

Newer GTA 5 players wonder why Los Santos is on an island.

Cayo Perico, GTA Wiki

I'm hoping to see multiple larger cities. Gta 5 had Los Santos and a series of tiny towns spread across the map and I think it made those towns essentially useless.

Los Santos Naval Port In GTA 5

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Dead Island 2 vs Los Santos (Grand Theft Auto 5)

Los Santos, GTA Wiki

Villa on private island [Add-On / YMAP]

GTA 5 New Cities & Islands DLC Concept - San Fierro & Las Venturas DLC Idea (GTA V)

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