The first reason the cryptocurrencies offer utility. You can use them to pay for services on apps that have been built on top of blockchains. Common ways in which people use their crypto are Gaming, (NFT) art and decentralized finance (DeFi). The second is that some cryptocurrencies offer rewards if you do stuff with them. The third is that some cryptocurrencies such as bitcoin have superior money attributes as a store of value. These three elements inform retail investors and financial institutions' trading decisions.