In 2008 USA Swimming held trials so close to the Olympics; (as they usually do), that when Jessica Hardy tested positive for a banned substance both Lara Jackson and Tara Kirk were not allowed to attend the 2008 Beijing Olympics despite racing clean for there was too little time to sort out an appeal, a clarification and most especially the politics... Lara Jackson and Tara Kirk were essentially robbed of a lifelong dream they both earned. [Link]
From Yahoo Sports:
Coughlin, who earned six swimming medals at the 2008 Olympic Games, acknowledges that there are arguments for and against holding Olympic trials earlier. She just doesn't necessarily agree with all of those arguments, she said.
For instance, the end of the college swimming season could interfere with trials, and some coaches believe that allowing swimmers to qualify for the Olympic team too early makes swimmers complacent.