If fat is the best fuel source, why is another fuel source needed for higher intensity exertions?
If fat is the best fuel source, why don't players fat load before games?
If fat is the best fuel source, what is the point of carbs?
Because while you can certainly handle high intensity exercise with high fat and low carbs, the body will cope better under that level of stress with more carbs due to more glycogen being stored in the muscles. Like I said though, it completely depends on what kind of carbs are consumed. The low GI carbs will be stored as energy for those big bursts, but high GI will cause an insuline spike and thus a crash where you'll feel fatigued and probably hungry quite quickly.
I do this myself these days, low carbs for most of the week when I'm working, going to gym, training, jogging/running etc. and I feel top notch. But playing an actual game (assuming I'm going all out and running my guts out) without a decent amount of glycogen can be a bit difficult, I lack that extra burst of energy towards the end and my muscles don't need as 'full'. Therefore within a day or two of my game, I increase carbs by adding foods like sweet potato, pumpkin, squash and less regularly bananas.
They don't need to fat load because their energy intake already revolves around high fat, whereas they save the bulk of their carbs for loading at the end of the week before their game.
Keep in mind, I dropped out of my sport science course in year 2 out of 3 despite having some good links, so I'm not as up to scratch as I want to be. But there's some good reading from guys like Darren Burgess (Port Adelaide), Tim Noakes (University of Cape Town), Peter Brukner (Cricket Australia) and Zeeshan Arain (Melbourne Demons) which would be a good and relevant start.
Edit: Here's a vid of Arain and Tom McDonald discussing it an answering some q's.