IMO bitcoin is a bit of a unique case in this sort of conversation. It was the first and every exchange uses it. It's the way most people enter the crypto world without mining. As a result it's essentially the gold standard for crypto (depending on who you talk to) which is where some of it's perceived value resides. It's the primary means by which you do other crypto business in the crypto sphere and as such has use as long as crypto has a use.