And it is quite possible to monitor if people are using FIAT. After all bank transfers, debit/credit cards and Paypal - all these methods can be associated with your ID.
With bitcoin it is a lot harder to track you or even tell if you are gambling online or not. And that is the reason behind BTC gambling boom.
Actually this raises a good point, another good advantage for Bitcoin will be that if you are not an adult you can still gamble with your money anyway.
I remember when I was a kid like 14 or something, I was in highschool and I wanted to play some poker on the internet, but the fuckers wouldn't let me join on the sites to play for real money cause it needed an id. If I was 14 in 2016 I would just use Bitcoin and have some fun in poker playing for real money, and even spin some on the slots. I could have made a lot of money back then but they wouldn't let play. Imagine being in high school and making money with poker, it would have been so cool but I was stuck with my parents small time cash pay :p