Couple of reasons:
- Repinning a lot of pins from one domain or one account
- Repining content that users didn't like so they were reporting you
- Obvious automated behavior - account working 24/7
- 90+ pins is a lot. Some users get away with it some don't
Regarding unbanning, you can try with appeal again, go here: https://help.pinterest.com/en/contact
In field "What do you need help with" choose "Getting into my account" and in "Tell us more field" choose "Appeal account suspension"
Now, scroll down and click "I Still Need Help" button. The form will show up on right side.
Fill it, say something like:
"I have no idea why you banned my account, please unblock it, all I was doing is pinning useful content to relevant boards!"
Fill your name, email and username below, and submit it.
You'll get email from them, it usually takes day or two.