Of course you get banned people, you think it's happening for no reason????
You have spammed tons of comments and done other spammy stuff before and IG knows that. They're not stupid. They are aware of everything. So, you're not getting banned for nothing. You must have done something in the past and you didn't cover your tracks good, so you left footsteps behind you and now IG is haunting you.
I, myself, run a few accounts and I am expanding everyday more and more accounts, but I NEVER SPAM. I mean NEVER. I keep everything on quality mode, I NEVER comment even. I find comments too risky. People want to grow too fast and that leads to bans. I'd rather be patient and wait than risk it all for a very little time difference.