I have no doubt that Brooks can find any leather they want.

The leather I've been using, to recover ruined saddles, is awesomely thick. It is from Mexico and is not especially noble stuff. More than one person (who know what they're talking about) have suggested it's too thick. Indeed it is so thick that I thin it a lot around the edges, which would make it very hard for anyone to actually measure it. But it makes for a very hard saddle. My saddles, when finished, are as hard as any Brooks I've ever held in my hands. The one on my commuter bike, with 2000+ miles on it (I have been using it ever since I made it in September) is still hard, though it has sagged and stretched a bit.

From this I would conclude that Brooks saddles are the way they are because Brooks has determined that this is what the customer wants. Certainly they could make harder saddles; but they probably get more complaints about saddles being too hard than too soft.