i agree that a large portion of the transactions are from the gambling sites but most of it is spam too and the amount of those transactions is not that big either so you can't really make a conclusion based on lots of small transactions that these casinos make.
most of casino doesn't spam,the ones that spamming the blockchain is a gambling site that synced with blockchain API for every transaction
but i'm still wondering whether if this spamming still keep up,whether it's gonna affect the entire blockchain?