Major factor to consider is whether a project has a working product/prototype/service or is just still a concept or work in progress. This could be fodder for extinction as non-operational altcoins are weeded out in favor of ones that actually have something on the table or have made significant partnerships.
Good analyse can be found here: https://www.newsbtc.com/2018/08/15/which-cryptocurrencies-will-survive-the-altcoin-apocalypse/