This is partly true. Crypto projects give away huge amounts of tokens for free through bounty campaigns and airdrops just to advertise their product. But the story does end here. The big picture is different. Crypto projects give high amount of bonus during pre sale or ICO or IEO. So investors sell off tokens just to get quick bucks right after hitting exchanges.
In fact, this is the main reason for the price reduction. Participants in the bounty and airdrop have almost no effect on the price, since they are paid very small amounts. The whole problem is the huge bonuses that are given to investors.
But this is not the main problem. The main problem is the lack of good projects. Naturally, unpromising projects will immediately depreciate.