Kara is 35. I saw her at the US 1/2 champs. She is still very good looking and could pass for under 30. But, by the time she hits 40, she is not going to look that good anymore. She knows that both her athletic clock and marketability clock are ticking. Nike will be looking for the next great US female runner who is marketable and will invest in that athlete. Nike will not invest much in a runner who has not been finishing well in big events recently and will not be patient with an athlete who is not running a spring marathon in favor of doing a few track events. They want someone on the line in Boston this spring, not at Oxy or USATF nationals.
Kara is likely looking for a smaller brand who will make her their flagship runner, like Meb did with Sketchers. That kind of relationship will let Kara run track meets instead of marathons and put her face out in the public more.