I'd guess: Because SpaceX isn't making Starship as specifically to go the moon but also for commercial orbital launches, because sending it to the moon involves

I'd guess: Because SpaceX isn't making Starship as specifically to go the moon but also for commercial orbital launches, because sending it to the moon involves orbital refueling which they might not have ready yet (or don't want to spend launch opportunities on), because they intend to have and operate more of them so the lost opportunity cost of not using a launch fully isn't as high, because the test flights to the moon are a NASA project (afaik) and they are waiting until NASA wants to do (and pay for) them, ...