It is simple economics. If the trials are held in Kenya, AK has to take on the expense and, even with strong sponsorship, will be lucky to break even. Pre-classic will pay top dollar to get the Kenyans to the US. AK will probably make a lot of money off of their trials instead of possibly losing money. If that money goes to improving the training conditions for Kenyan runners, then it is a great move. If that money goes into the pockets of the corrupt AK officials, then it might be better to just have AK lose money instead.
But it will be an amazing race. The Kenyans are at an unfair disadvantage at the Olympics in that they can only bring 3-4 of their best. An injury or two and a bad race or two and the Kenyans could lose out on medal spots to inferior runners. This might be the only time a full field of Kenyans goes up against the rest of the world. We will really know whether the rest of the world can really compete with the Kenyans.