What are the main reasons for an Amazon account being blocked?

This one depends on when it was blocked.

If the account is blocked as soon as you apply, it's usually because the information has been used, the internet connection is not clean, and the account is linked.

After that, there are basically the following situations:

Still associated with the account (detected)

Performance is too poor (high rate of bad reviews (feedback), return rate of refunds, etc. and service-related)

Infringement (the consequences are very serious, the first time the plot is not serious, may just shut down the listing, but after that ...)

Reviews are serious

If it's a European site, it could be due to VAT