If there is free money involved, you will always have people that want to cheat the system by making multiple accounts or doing something else. It is the same for all giveaways that casinos do and not easy to stop it or to detect everything.
Yes, in fact such people always try their best to cheat the systems when it comes to free money. The simplest way to cheat a system is to create multiple accounts and those cheaters know that thing and that's why they try their best to crease as many accounts as possible in order to cheat the system and earn some free money.
I think that's the main reason why casinos set wagering requirements for bonuses because a cheater can't complete the wagering requirements most of the times and end up losing instead of winning. Same rule is applied for giveaways in order to stop those cheaters.