At the beginning ...
The idea behind framesets is great. It's alive and kicking today; check StackOverflow's left side panel, or the header. They are fixed divs, which is basically the same thing as having frames, although a lot more flexible.
The very concept of keeping some part while changing another is simply necessary by the logic of webpages. We need something to stay where it was (typically navigation) while we go through a lot of details in the main area. Framesets served this purpose very well, they were easy to use and fully supported by all browsers, meaning 3 at that time (Netscape, IE, Opera).
Then we scorched the sky
The real, practical problems with frames had nothing to do with their basic concept. Instead, it was us being only human. I followed this whole debate very closely so believe me when I say these were the real charges against frame technology:
Designers hated them.
Yes, that was the deadliest punch. Everything looked square and straight. They hated it. They wanted arcs and image backgrounds and rounded borders. Now they have it in CSS3 - guess what, they're drawing squares. #whatever
Programmers had trouble with them.
It was inconvenient to follow the logic of frames, and you had to do some extra work. I mean, some. Today it's a lot harder to create AJAX solutions for the same problem, but no one complains. #whatever
Websites could include one another.
This was painful for some site owners because they worked hard on something and another fella used it as own content. Later, they invented same origin policy, but it was way after starting to hate frames. Content stealing is still an issue today, absolutely unrelated to whether we have frames or not. #whatever
Back button worked differently.
Yes, it was a bit annoying. But it was not the frame concept's fault, again: it was browsers who did this to us. Could have been solved easily, but nah, browsers kept going back one by one, not providing the site a way to implement its own "step back" method, and alas, this is still happening today. #whatever
So instead of coming up with a solution, the world's web developers decided to hate frames. They ditched it, and now we live in a world where there are lots of better solutions - but with a lot more effort. This was not the only feature going thru the hate-ditch-reinvent-love cycle; see vertical centering and flexbox, aka the table tag debate - and it will happen many more times because it's always easier to point fingers at something than to learn why it's great.
I don't hate frames; don't miss them either, they belong to a somewhat outdated world of web. But they were a good solution for something, and there's a chance we'll see something similar in the future just as CSS grids came back to implement what table layouts did before. The same community who hates the old solution will happily embrace the new and tell you why it's not the same at all.
I think this story has a single takeaway:
Implementations come and go.
Concepts stay and evolve.