I don't know if this just sounded like a zinger to you when you wrote it, but "the Internet" is a prime example of anything but a solution in search of a problem.
ARPANET/the Internet was developed to facilitate communication, remote access and data sharing between different computer systems. Are you sticking with "Why not just use a phone?".
20+ years ago the majority of the world had little to no understanding of the internet. People with technical backgrounds may have had theoretical ideas about how connecting the world online would radically change it. But it was exactly a "solution in search of a problem" in the same vein as decentralized computing through blockchain technology is today. A world where the digital world was as critical as the real one seemed ridiculous on its face back then.