I believe you don't get any campsite villagers/island tour villagers if you are at the cap of villagers living on your island.
i've had campers at full capacity on my island and they'd ask to kick someone out if i wanted to invite them!
Were they amiibo campers? Cause I know you can kick them out if you have an amiibo camper. Not sure if you can if it's a random visitor.
I barely get them too. Like maybe one every three months. (TTing)
they weren't amiibos! random visitors let you kick residents out too