How come a promotion is a scam?
Promotion is just a marketing strategy to most businesses including the gambling casino, their main target is to attract lots of customers to play on their casino. The offer may seem to be smaller to you but for the other gamblers, it is enough already, at least they got some bonuses with that promotion. It is up to us too to find whether we like to play on that casino or not since nobody is forcing you to play on that site.
He didn't said all promotions are scam. It's possible that some promotions could become a scam because sometimes casinos hide the terms and conditions of the promotion and could suddenly add an extra rule once a player starts winning too much than expected. I agree that we're not forced join a promotion but it's hard to avoid when it seems like free money.
Most of the time promotions won't be getting termed to be scams, in promotional marketing scams were commonly experienced with bounties. As every process is associated with internet even legit way of promotion go as a scam. Recently one happened with icoforums.net, which was growing good with better way of promotion and served the participants good. In the mean manager took away the funds and ran away.
All the gambling sites should have promotions because no such business should ignore this major point to become a successful one. The major points to consider are the product, place, price and promotions which are strictly focused to have a successful future business. In case of gambling all the sites which are running on the internet services are not scams and should have promotions but scams also exists.