Saying that withdrawing big money will bring players into trouble is not entirely true because you can see in rollbit a lot of whales players who will definitely use big money to play and the wins that will be obtained are also very likely to be huge and none of them complain when they do withdrawal means they can receive the money smoothly.
It is not true. Withdrawing big money is nothing serious if the casino is legit and has deep pocket to pay the user. They should have budget to pay users when they launch their business. Without such deep budget, they can turn to scam anytime especially when they suddenly have to approve and proceed big withdrawal.
Only players who are suspected because the casino sees suspicious activity that will get him in trouble, as long as the person is playing normally and doesn't break the rules then it will be safe.
Casinos have to pay users for win bets so they are not tolerable against suspicious activities and activities which go against their Terms of service. It makes sense as if they are not strict with it, they will open gates for bad users to compromise their platforms.
Also I can't understand why there are players who do multiple accounts at a casino, I don't understand the benefits they will get by doing this, unless the casino is holding promotions such as bonuses it is very possible for players to abused by doing multiple accounts, but multi accounts for normal play makes no sense in my opinion.
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.