I can consider it as manipulation, it always happening where certain coin does not have any more uses and can be called as scams but the big players (whales) are usually pumping those coins where they putting huge margins in the bottom for the price to manipulate and it can go pump. When the traders and some investors saw it, they are entering in that coin while the whales are starting to sell their position that may cause huge dump and losses for some investors and traders. As a trader, I avoid those kinds of coins because it is a double edge sword for me. Yes, it can give me huge gain in the short term but one wrong move, I'm aware that I can lose huge amount of money so it is better if I avoid it.
yes. normally, dead coins would be delisted somehow, or sometimes being cellar boxed. it is more likely someone closed his short positions that affected the others into domino effect. these coins, even if you could trade it, better not engaging it at all or you could be end up yourself in trouble (saw some coins dropped to near-zero in a matter of day).