The problem with Sam's side story is that it's the sort of thing you start with a few more seasons left to develop it. It's one of those plots that spreads the story out and introduces more character, locations, and narrative arcs to be resolved later.
That's not really where they're at right now, in a narrative sense. They're trying to close things out, and that means the characters they've spent so long spreading out need to be coming together, the number of plot-significant locations needs to shrink, and any plot threads that aren't tying into the finale need to be getting tied up as neatly as possible.
So, you know, I understand why they did it. It was kind of dumb and made Sam look kind of dumb, but from a perspective of, "This character is popular enough we want him to be involved in events, but we can't really afford to keep spending time with him effectively by himself", I get it.
