Because people have stopped believing in the teams of Altcoins. The team may do anything to increase their profit or may try to do exit scam. Potential development of most of the coins are less these days and making a sustainable platform and use case of tokens are rare.
Of course, the same thing is happening with the developments coin, we are seeing many fake coins are failing to survive in the market because we don't see any active developments from them but potential altcoins are also decreasing their even though we see active implements from them. I hope they are decreasing because of Bitcoin fluctuations.
