Many altcoins died because they don't have a real usecase, their token is useless and their team are not hardworking enough to make some developments and partnerships regarding their project. Altcoins that have a bright future and we might see in the bull run are the one's who doesn't stop on developing their product no matter the condition of the market and their team is focused on making their ideas possible.
A large number of altcoins are copycats and the only intention behind their creation is to bring profits to the promoters. And therefore it doesn't surprise me that many of them died down. Good altcoins with practical usage are still being used in good numbers, and one example is that of Litecon. Despite the technological disadvantages, the development team has been working hard to remove the bugs and issues and the end result is for everyone to see.