Specifically for 10K it's hard in general to get American women capable of pacing through 5-8K at world standard paces. The top women of course can manage those paces, but there's like 5?ish of those people. Most of the best college women are barely getting to 15:15 minutes 5K. And the pros capable of doing those paces are either wanting to actually race at that pace, or save their legs for future races / other events. It's a combination of a very unpopular event and few people capable.
At least with 5K, the pacers only need to get through 2-3K which a lot more people can do. Even a failed pace job that only makes it 1600m isn't as big of a disaster for a 5K compared to the 10K.
They would have had to shell out a lot more money to get some strong international pacers while also paying them enough to make them waste 1 week that they could be training at home or racing for money.
I think OAC even mentioned they were struggling to find a pacer for 10K, and this event was announced for a few months beforehand.