Cryptocurrency trading is so volatile and decentralized that no regulations are applied to it that's why traders can do what they wanted. Pump and dump always happen in crypto trading because of the low volume of coins that those traders who hold large amount of coins can make the market move. Those traders that hold large volumes of coin are called whales and sometimes when they buy a coin, it would make the price shoot up which is a pump and they may continuously do this to attract other traders to buy also because the price is rising and they will create FOMO of it like releasing a news or updates that would make others buy the coin and then later on when it hit their target price, they would slowly sell their coins already in profit and in effect would make the price go down or being dump.