I can think of several reasons.
1. How many successful launch/catches of the booster will the government require before they allow a catch at the KSC?
2. Will every booster move require a Starship for every shuttle flight? There will be far fewer boosters (supposedly able to launch/recover/launch several times a day) whist many payloads will be tankers, moon landers etc unable to be caught). If not, then unless a booster only profile is developed the boosters will need to to moved on a barge.
3. There has been discussion of shuttle flights for the Staship, which is pretty robust. But a lot of the structural integrity of the booster will be provided by the fuel load, which also relates to the G load during launch and max-Q; can it launch will a partial lot without breaching those limits? If a full load is required what will be the flight profile? The path of the Caribbean is now proven, but one inclined to the north to allow a burn-back to land at the KSC will presumably overfly or go near Cuba, the Bahamas etc.