You have to question almost every post you see about crypto, since everyone is just out there to make money. You don't see people stopping you in the street to give you investment advice since there's no incentive for someone to do that.

By telling someone to buy a crypto, you hope they buy to increase the price of the coins you already have. By spreading FUD, you hope to drop the price- either so you can buy, or so something else you're invested in looks better in comparison.

People who want crypto to fail are obviously not invested in it, but they are invested in other things. They want to lower overall competition.