I think that runners like El Guerrouj, Geb, Silva, etc. run indoors instead of XC because they are much more likely to win indoors than on XC, and because they'll make more money for it.
Only now, in the last two seasons of his career, is El
Guerrouj giving XC an honest go (since his junior days).
Possibly, but I am fairly confident Bekele gets a nice sum for winning 6 X-C titles.
As for likelihood of winning, the very best in the world should be selecting the most competitive races, not the ones only where they will win. If they are indeed the best, they should be looking for the challenge to expand their own limits, not taking a paycheck and a tactical indoor win (the WRs indoors are comparatively slow in most cases, even for some of the "fast" races; 1500 "only" 3:31, whereas El Guerrouj has compared running some 3:29's in the Golden League to "jogging").
Outdoor track really seems to generate far more interest among worldwide track fans.
Outdoors there are more events, faster times, measurable progress (World and Continental Records, etc.), more championships and possible medals, better crowds (especially in Europe, as in Zurich where the crowd applauds the whole 5,000m) and a different atmosphere.
For me, it is not surprising why Kennedy picks outdoor as his one and only focus.