But we have to buy only good market capitalization coins. Don't invest money in shit coins.
It is not necessary that if a token/coin has high market capitalization, it means it is worth it. If a token with a total supply of 100 billion gets listed on a shit exchange where you see buy orders set at price $0.0001 and sell orders at $0.01 and if just one buy order happens, it will ultimately bring its market cap to 1 billion USD if coinmarketcap has that token listed there. So this is a subject which needs enough of research to invest and find those good tokens which will give better gains.
Actually, you are talking about a bug or a distortion that can occur on Coinmarketcap. This type of situation happens very rarely, and as far as I know, this is mainly what pranksters do. However, many people fall for it without carefully checking the situation. Anyway, these are only temporary errors and do not help the coin last longer. If a project doesn't develop, it will die sooner or later.
The amount of coins on the market is still increasing, so we will not even notice that several dozen or even several hundred disappeared during the year.