Care to elaborate? I genuinely just don't see it.
Well, this isn't a spoiler thread for either series, so it gets a little tricky in going into detail. I'll keep it relatively vague, but if anyone is avoiding spoilers for either series they shouldn't read this post.
In both stories you have two royal houses go to war, both authors drawing on similar historical sources no doubt, but you also have the details of a noble lord who is drawn from his safehold when he accepts a new position and an inciting incident that kicks things off. The noble lord's wife initially married him out of duty, but came to love him deeply. The royal houses have advisers trained in arcane knowledge - mentats and maesters respectively.
You have characters on a Hero's Journey who go into a wasteland, bring together disparate tribes, while mastering their own mystical abilities, aiming to use those abilities and the forces they've marshalled to get revenge for what was done to their families. There is a prophecy of a messianic chosen one.
You have assassins who can change their appearance and a young female character of the noble house (or at least comparatively noble) on a dark path that involves the assassins.
There are some additional elements, too, but those are the main ones I can think of for now.
A lot of these are common tropes on their own, particularly the Hero's Journey and chosen one points, and there are other influences at work, too, and points of divergence, but there are enough structural similarities in the combination of some of these elements, particularly early on, that I think Dune
was a key influence on Martin.
The material is there if you know how to utilise it. 'The Walking Dead' managed to extrapolate a whole season out of what was just a handful of issues in the comic.
As I said, you'd have to massively expand on the first book to fill it out to three seasons, so, yes, it could be done. I'm not saying it couldn't. But it would be very tricky to get it right and I don't think it would be the best approach.
And I don't think straight adaptations are redundant, any more than rereading a book is redudant. They're a means of enjoying the same story over again in a different medium utilizing that medium's particular strengths (which often calls for at least some adjustments to the source material).