Speaking for myself, when I got into traditional shaving about 6 months ago and started shopping for a razor to replace my cartridge razor, what I found were DE razors and that's what I was familiar with since my Dad used one. I had jumped in before I discovered B&B or other sources of information, though I did refer to videos to help me understand technique (thanks Mantic!).
I didn't really know SE was still an option until I'd been at it for a few weeks and was more actively reading this forum. Since then, I have looked at SE razors and am intrigued, but I'm not a vintage razor guy, so options for a new one seem somewhat limited. I love the look of the Mongoose and may try that one day, once they are more readily available, but for now have a couple of DE razors I'm happy with.
+1It might well be because there are no off the shelf or currently in production models - it's an entirely vintage thing and only really having taken the first step into traditional shaving via DEs does a person really find SEs. So, a small few of a small few ...