It's not the existence of crime, crime happens in real money, too. It's the complete and utter lack of anything else but crime. Originally, Bitcoin only appealed to 1) geeks who enjoyed the technical details and 2) people who wanted to buy drugs. Then, you got to phase 2, where bolstered by the liquidity provided by the people trading drugs and the unbridled enthusiasm of the geeks, the value went up. Then, The Silk Road got shut down, and the value started to fluctuate wildly, leading to runaway speculation, attracting the "fight club for finance" guys. Those guys marketed crypto to the broader flock of normal people, because they needed bag-holders for their (illegal securities trading) schemes. The influx of people gullible enough to listen to the finance bros provided a pre-filtered pool of people who would make good marks for scams.

The useful applications of crypto are illegal (buying narcotics) and the majority of the ecosystem today is both illegal and completely economically nonproductive.