I'm not saying rotation is a stupid idea, in-general. However, in AGoT it doesn't accomplish what you want it to do. Think about it. If you identify all the things that are frustrating, confusing or unintuitive in Thrones, you'll quickly see past the card pool and notice a inconsistent, fiddly underlying mechanical system, with poorly templated cards and often incomplete or unsupported design ideas. (re: arcane timing windows, no action before dominance… except shadows, and so on)
More importantly, new problem cards enter the pool every cycle. Just last week, debate came up about Darkstar being able to be targeted by effects triggered from cards that discard him into play for their cost. Even if Darkstar were rotated out of the pool, the very fact that this kind of card interaction is even in question so many years into the game's life has implications for so many things to come.
In reality, thrones IS a messy, convoluted, difficult to balance train wreck built on top of layers of of legacy design. The only way to fix that is a total reboot with rules and card functions that are more approachable by the general audience.
That's so expensive and risky it's not likely to ever happen, though there's always a chance it could