The market has realized most of these coins are worth nothing and the promoters have no intention of developing the ecosystems
Those altcoins that drops into zero value has developers that did not create a good marketing strategy in order to get more investors in the market, so the price has drastically decreases.
Marketing has nothing to do with it. The creators of the projects did not have the goal of their development, they wanted to raise a lot of money, so most of the projects do not develop.