There are many reasons. Except bad intention to use multiple accounts to cheat the casino including bonuses, free spins, etc. I think there is another reason which makes sense. Like you have an account on the casino but didn't use it for along time. You forgot registration information of that account so when you want to use it, you create your second account which violate most of casino rules.
The safest way is to open a support ticket and go first to ask the casino to check your existing account as well as will they accept if you open your second account. Some casinos can support you to deactivate your previous accounts.
As long as you're still have access to the email you used during registration, you're fine because you can use forgot password to set up a new password.
You're correct, asking the live support about your matter is the best thing in order to prevent anything ban that could happen. Like want to create a new account due to can't have any access to your old account, asking to allow VPN usage since the ISP block the casino etc.