I guess they make money by referral reward, not sure how the referral reward in centralized exchanges because it varies from one to another. But, I think mostly they earn from someone else lose, so the mentor will ask to sign up with their referral and make deposit, then they will teach their skill, either it's a fake skill or real skill.
In this way, they're making money without need to ask the followers to buy their course.
Referral programs are a separate topic, but yes, it can bring in very good money if you approach this issue thoroughly, if there are enough referrals, then such a person will receive his % from each purchase and sale, no matter whether these are unprofitable or profitable transactions. The exchange works in the same way, it will take its fees from any transaction, no matter whether it is profitable or unprofitable, this is the principle of their work. But for a teacher it is important that his students can trade with profit, otherwise there will be a lot of negative reviews about him.