I know of two people that opened multiple betting accounts but their interest was not exactly having multi-accounts to play but to try to arbitrage spreads when they could find a game or a bet that had a very tiny spread or even a "sure bet" by betting opposites in both houses. These multi-accounts tend to last only a few months because the betting houses tend to catch and ban the creators.
^ I have a little confusion in my mind on how they can catch the creator of multiple accounts, the same owner on different devices will most likely hard to catch it. It should always be good to read first the TOS before using the casino, some casinos don't mind having multiple accounts as long as you did not abuse it. On my side, why not just focus on your one account and made it become a VIP member, so that you will have a lot of bonuses and rake back if there is and other promos that are intended for those members who have higher wagers.
Reasons on why people do make out multiple accounts.
1. Abuses promotions and bonuses
2. Does like to have a new account whenever they got busted on their previous account
3. They totally forgot or doesnt have any access on that old account
4. Simply just like to create new.
Reading up TOS is always suggested but even with this basic thing people do always missing it out.
so you missed one of the reasons: Bookmakers CAN'T beat some bettors, so their best idea is to block them. I'm one of them and:
1- I dont take any bonus or promotion of any bookmaker
2- I got limited because of winning too much.