Good point, I forgot to mention the email part. I kept all the accounts with the connected emails (I placed them in a set and forget folder in case I ever needed them again).
I'm not sure if IG/Facebook (Fb owns IG) locks the accounts, my best guess is it has something to do with updates. Because there was frequent updates to the IG algo within the last ~six months, I'm assuming that affected the bans/verification looped accounts in some way.
That's my best guess anyways.