Remember before Web 2.0 when many pages were just static collections of data. If there was some sort of read-only interface to a website that didn't need to be encrypted, that could be implemented along-side of https. Remember RSS? of course, RSS was just an additional data file retrieved via HTTP, not itself an actual protocol.
HTTP stands for "hyper text transport protocol". Somehow, this got turned into the default protocol for everything on the internet. So instead of visiting an HTTP site to retrieve static content, now you got to an HTTP site and it might ask you for your credit card information. Someone said "this is insecure" and added secure-socket-layer (SSL) to the protocol and gave us HTTPS. In restrospect, perhaps a different protocol for truly secure bi-directional communication should have been created? HTTPS should NEVER have been allowed to fall-back to HTTP, but because it was an addition to HTTP, not a different protocol, it was insecure from the start. Now we have an entire internet barely able to handle security.
And before LetsEncrypt, the process to even setup HTTPS was expensive and complex. Luckily that's been eliminated, but the HTTP:HTTPS cross-dependencies will basically mean a lot of insecurity until HTTP goes away or a viable successor just replaces the whole thing.