sometimes they don't want to teach their friends for a reason that they would earn better or more
Incorrect, someone don't want to teach his friends because he worried if his friends will blame him after his friends invest in cryptocurrency. Or his friend will ask money because they know you're making a lot profit from the crypto you told to them before.
Actually teach friends to invest in crypto will make you earn more because the demand of the coin is increase (in case he buy it).