There could be a couple of reasons.
1. The broker doesn't want its traders to be exposed to high risks correlated to crypto trading. We all know how volatile cryptos can be and how fast they can divide the deposit by zero.
2. Next one is that FXCC's regulations don't allow the broker to implement crypto assets. Right now some EU regulators are very strict with cryptos. Not just trading but also using them in day to day life.
So if you want to know the truth you can ask the client support, but does it matter? The broker offers enough instruments to trade with and make money.