This is dependent on the betting site.
Some sites offer a limit between 10-20 individual referrals, other sites cap the amount you can claim to a certain amount each year - but if you've got a bunch of friends that want to sports bet, then you absolutely have the chance to earn tons of bonus betting funds.
Example: PointsBet doesn't limit the number of referrals explicitly, but they do cap the total amount you can earn each year at $2,500 - which is a hefty sum for just having your pals sign up to an awesome betting site!