I'm not sure about the typical riad bike punter- my background is Mountain Bikes and thats where the orders are coming from. Those modern carbon frames are so well dialled for both comfort and speed but i find them rather souless.
However, there is a move away from 'the man' amongst certain types. It was probably the fashionista fixie types that have restored vintage Hetchins frames and the likes, and outfitted them with newer groupsets to make trendy commuter bikes that have started a trend toward more traditional looking bikes. There are some really cool younger builders like Ricky Feather springing up that are building great frames with modern handling but with beautiful traditional touches. Steel tubesets have come on in leaps and bounds in the last 25 years and you can now get a frame that handles like a dream and has that classic steel spring, and looks nice to boot. I suppose its about individuality and nostalgia more than anything. I suppose they are the cycling version of those new old Morgan 3 wheelers- very niche, very expensive, not terribly practical but a whole lot of fun. And if there is anything we need right now its fun!
Plus you look cooler riding a traditional bike when you pull on your classic woolen Rapha gear.
Mate of mine did L'Eroica a few years back. Said it almost killed him but it was the best fun he has ever had with his clothes on. I really want to have a crack at it one day.