Well, when I bought my CPO X1 35i, it was a little orange fireball sitting in a sea of white, black and grey on the lot.
I think the X1 is a great choice, but not everyone wants a small pseudo SUV/wagon. Personally I love wagons and have owned a bunch over the years.
But wagon's have been a harder sell here in the US than in Europe. Mine is an X Line and will get a small slew of mods going forward.
I don't think the X1 is unpopular, it is just one of many BMW buying options available. The price is very attractive for what you get, but someone who pulls into a BMW dealer usually has more $$ to spend than the X1 requires.
Me, I didn't have the bucks that a BMW requires and I didn't expect to find anything on the lot. The X1 wasn't on my radar at all but there ya go!
Here in Olympia, there are 2 others that I have seen. A white and a metallic bronze. Both driven by middle aged women. Sigh...I have a chick car...