Few reasons why they decide to create 2 or more accounts.
They want to increase the level of their accounts and take advantage on the benefits they get from it.
Referral fees if there's reward given on their sign ups.
Can you explain how and what two accounts must do to increase their levels? Isnt it only the more you wager the higher level you have strategy? It must be something related one account making a deposit, but other not. Otherwise it wont make any sense.
Referral thing looks also lack of sense for me. From my experience, people get referrals by promoting their ref link and earn % of what those referrals lose. Making lots of accounts to get a cashback as a % of our other accounts amount lost. That is crazy. And stupid. Risk own money to get a cashback.
I could understand that there might be a case, when a gambler completely forgets his account name and email used, so he creates another account. And during KYC, he is being caught that such ID were already used by other account. But probability of such thing to happen is very low.