Why would that be hard? It's used for tons of illegal activity (ransomware as an example).
It'd be hard because you'd have to find every single node and disconnect it from the internet, and something like 90% of Bitcoin nodes run over TOR
And you know this... how?
Did you know that 96% of statistics are made up on the spot?
Here's a source if you're curious
Also, can you provide an article showing that Bitcoin is used for "tons" (whatever percentage tons means) of illegal activity?
Bitcoin is used daily for remittance payments, which is huge since it's way cheaper than sending money through western mutual
There's also Bitcoin Beach in El Salvador which is a bitcoin only circular economy
Paxful provides a service for people to trade gift cards for Bitcoin