Currently on the coinmarketcap site only about 1590 projects compared to at times more than 1700 projects. They have left many projects without developers or scam projects. I personally invested in some of these projects and lost a lot of money like bitconect and centra. Do you trust the projects you are investing in and will keep them for a long time until they succeed or are they just looking for profit in the short term?
It was normal for other projects to die since not every altcoin in the market is being invested, the competition is keep on growing and every developers should have different strategy to make the price of their coins increase in the market.