why won't girls stop contacting my boyfriend?

Since the beginning of our relationship people from his past keep reaching out. He deleted any girl he had any kind of non platonic thing with a while ago, but since the beginning it always seemed like people were trying to reach out through text or Snapchat. It's still happening, he will just get random numbers of people who aren't in his phone coming back. He told me at one point he was talking to hundreds on tinder and he goes to bars a lot and it just makes me so uneasy that girls are still trying to contact him even though they haven't talked in a year or more. Why are they doing that? He's been deleting the messages or so he says but it just bothers me that it always seems to be someone else and it never ends.
I brought it up to him and he swears he's talked to no one. They're just random numbers that pop up once a month or less or so but it's just annoying because there are so many and it's been so long!