Blockchain and cryptocurrency are two different things but they are inseparable. Cyrptocurrency is digital currency which can be used in financial transactions and those transactions are automatically recorded in digital ledger called blockchain. This is same with the existing accounting principle. Every transaction should be recorded properly for monitoring and transparency of records. The good thing in blockchain is, it is made publicly and cannot be corrupt by hackers. In this manner, you can see that in every cryptocurrency there is always the blockchain.
True, but OP's question was actually the other way round: Not "cryptocurrency needs blockchain" but why a "blockchain needs cryptocurrency" (which is not the same thing logically!).
That was already answered well before: At least in a
decentralised and permission-less blockchain, you need the cryptocurrency to incentivise miners and get the game theory right (i.e. so that there are economic incentives to stay in consensus with others).