What I still fail to understand is, how can someone make any kind of profit by creating multiple accounts?
Were they farming referral bonus? But given how there's almost a 10%~15% house edge on sports betting, it's impossible to farm a referral bonus. Maths won't add up.
Different players have different limits on how much they can wager. If they think you've found an edge somewhere, they lower your limits for those types of matches. One way to get around the limits is just make a bunch of accounts.