I ask this question, thanks in large part to what I’ve learned by religiously reading your tumblr over the past year: Would it be fare to assume that the Lannisters, post Conquest, never rebuilt their fleets to those glorious standards of the past as a result of the Iron Throne having the sole right to mint coins? The only surviving navies (AC), comparable to BC standards (IB and Arbor), both protect/facilitate their regions economies, while the West do not (to the same degree at least). RSAFan

I don’t think that’s the reason – Casterly Rock clearly has the financial capacity to build enormous fleets, given the money it’s loaned the Crown over the last 40 years. 

If I had to pick a cause, I’d say that there was a political split within the elite between those favoring a naval strategy and attendant investments and those favoring a land-based strategy and attendant investments, similar to that which happened in Classical Athens and other places. And these splits tend to be regional and class in nature – naval strategies empower coastal regions, port cities, merchants, whereas the cavalry-intensive armies empower the nobility and rural areas.