Seriously, I think it's because companies sell them to us.

It is convenient to have something to handle generating wallet addresses and sign transactions. And it is easy enough to load a wallet seed onto a hardware device (or into software) long enough to do that when needed.

But that isn't easy to understand for a novice. We're still trying to save them by getting them to move their savings away from casinos and custodians.

Any true long-term storage should be on steel or something independent of software OR hardware. I'm also liking the idea of representing seed phrases as RGB color values, and then using some kind of hillbilly steganography to encode them into an image that can be stored in decentralized storage.