ORIGINAL: noname-RCU
For a number of reasons: I've never heard of anyone competing in TOC, XFC, etc. using BME, I haven't seen near as much BME publicity like other engines, I've never or heard first hand info of anyone using them, etc ...
The reason that you haven't heard about them in the TOC is that all those planes are large, 150cc class and bigger. The largest engine BME makes is 110cc. Regarding the XFC, Jon Leyland finished 5th last year and has been invited (and accepted) back to this year's competition. He flies a RadioCraft Extra using a BME 102cc engine for power. Again, most of the planes you'll see in the XFC are 40% planes (but Jon doesn't care, right?).