Why won't my boyfriend bring me around his friends?

We’ve been dating for close to 9 months now and I’ve maybe met 4 of his friends. I bring him around my friends all the time, invite him to parties, etc. I’ve brought this up to him a couple times and he keeps saying that “they’re busy all the time.” Yet he seems to find plenty of time for them. I just have no idea what to do at this point.