Monero is a privacy focused coin that makes it popular to people who wants their payments to be untraceable. And Monero is so much effective in that sense that it is one of the most used coins for people laundering money, funding terrorism and providing illegal goods and services. It's the coin of choice for darkweb marketplace. It is often associated with crimes and hence considered a criminal coin.
That's why it's a prime target for law enforcement agencies. They are doing all they can to crack down and stop the use of Monero. They have made it such difficult to buy and sell Monero that normal traders and investors who have nothing to hide don't bother taking the trouble of owning it.