It's All Because of the Books
What makes Game of Thrones' confusing geography so weird is that it comes from such an assured place. George R.R. Martin's books go to great lengths to paint the scale of Westeros, with real time taken when character and armies traverse massive distances - that Winterfell-King's Landing journey is even more prolonged in print. When that sort of lateral thinking is inherent in the story, it's frankly perplexing that HBO can't get it right. But it's actually because of Thrones' nature as an adaptation that we now have a problem; specifically, that the show has now overtaken the books that inspired it.
Now, it's not that showrunners Benioff and Weiss are simply making up new stories without consideration for location. Their game plan for Season 6 onwards (where the series fully passed the source) is heavily influenced by Martin's notes for his unfinished final tomes. Exactly how much won't be known until when (if?) The Winds of Winter and A Song of Spring hit shelves, but it's fair to assume long-baked reveals (Hold the Door and R+L=J) and cataclysmic turns (Cersei blowing up the Sept and becoming Queen, Jon reclaiming Winterfell) are part of the plan.
However, because so much has been trimmed or completely changed in the adaptation of the earlier seasons (after Season 2 major leaps and shifts became commonplace), while these major events are set, the connective tissue between them varies massively. This means the routes that characters take to these landmarks events are smudged and dilated, which when you're lining up meetings with others leads to timeline and location contradictions.
It's all a result of taking an epic novel series and trying to dramatize it in any conventional manner. Part of the blame falls on Martin not being finished and thus D&D not knowing which elements to cut or keep, although really it would always happen when you're dealing with something on this scale.
Why It Doesn't Really Matter
All that said, there's a further quirk more specific to Thrones and its ilk that explains why we're talking about this at all: people know Westerosi geography better than they do our own. All the recent focus on the show ignores that this sort of weird jumping of locations with illogical travel time is prevalent across all movies and television. We just don't notice the constant redefining of city layouts (see The Mummy's approach to London) or quick cross-country jumps because most audiences don't know real world layouts to the same degree, and those who do accept the storytelling purpose behind it.
With high fantasy worlds, things tend to actually be more rigid because it's something built from the ground up and thus entirely the product of the work's author; you can obsess about every detail in Middle-earth as it enhances the experience of The Lord of the Rings, whereas having a Queens road map doesn't elevate Spider-Man: Homecoming. The same is true of world history; biopics play free-and-loose with facts whereas the likes of Star Wars have to get everything correct to a tee. Thrones is only standing out because it's not being as militantly faithful for reasons already established.
With that considered, it's a minor flaw rather than a damaging problem. Even watchers with an immense knowledge of the lore won't necessarily know the full geographic scope without reference, meaning the majority of Thrones' mammoth viewership are probably unaware of where exactly the cracks lie, or at the very least don't care enough to complain heavily. The show's got great drama, what does it matter if things are flubbed along the way? It's a trade-off; with shorter seasons to enable bigger spectacle comes a zippier pace, which in turn requires the dropping of several wheel-spinning scenes per episode worth of story.
The reaction to Season 7 is, as stated at the beginning, incredibly positive. Game of Thrones is delivering on promises made as far back as Season 1 and there's no indication of it letting up. To do that requires playing a bit more lose with pacing, so, when you get down to it, the geography mess-ups are just a byproduct of an accelerated storytelling that aims to hit as many narrative beats as possible in the time left. It's confusing, yes, but it's all in service of making a better show.
Game of Thrones continues on HBO Sunday August 13 with ‘Eastwatch’.