Not a rocket scientist, nor do I have any hard numbers, but off the top of my head the Moon has a much smaller gravity well than Mars or Venus. On Mars, you would waste much more fuel just getting back into orbit. And Venus is just comically toxic. We weren't even able to build a single probe that lasted more than a couple hours on the surface of Venus before corroding, much less a permanent settlement.

Also, the moon is only a few days of travel away, instead of months-to-years (so someone on a permanent base could be medically evacuated if they have a tricky tumor, say.)