Its because most of altcoins (hundreds of them) are really exactly filled with uncertainties. Whenever I look through websites of new altcoins I can find dozens of red flags. Coin distribution maths are generally very bad and sometimes look intentional so developers can get rich over investors. Sometimes whitepaper are very messy and amateurish. Only top 10-20 maybe 30 altcoins feel safe to invest.
yes, you are right, because many altcoin that have sprung up at this time just want to steal investors money (although not all of them), but we must still be careful if we want to invest in altcoin, because if we choose the wrong altcoin then of course our money will be lost, but if we choose the right altcoin, then of course our money will increase very much (get a lot of profit).
A project will rise if they are still currently developing or has a product that are active and currently service it's utility, I don't think there is a low chance that devs will try to run and abandon their project development in a bear market where their project didn't reached it full potential though this only is applicable to those project who has gathered the community trust and is being anticipated for. Remember that no one will buy a dead/abandoned/project that has no project updates unless the investor is a Degen. No buyer means there are no chance of it rising up even it's a bull market.