OED wrote:
What it all comes down to is that the cross country Americans grow up running is not the same sport as international cross country. Different distances, different course layouts, and different seasons. For Americans, cross country is a fall sport that is followed by indoor track in the winter and outdoor track in the spring. It is a regimented schedule that is second nature to Americans by the time they get to college. The world cross champs, however, are almost always held in March. No American grows up thinking about cross country in March. Their focus is two seasons on at that point.
This is a pretty weak argument. High school / college athletes spend summer doing base training for XC, yet somehow they're able to adjust as pros and treat summer as peak track season. I think they can handle a similar timing adjustment for XC.
I'm less familiar with the historical trends, but when did indoor meets really start taking off in popularity? As a high schooler 20+ years ago, winter was back to base training for track. Maybe you hopped in a local indoor meet, especially to get your legs moving in snowy climates, but more likely you did base and maybe broke it up with a 5k road race sometime in Jan/Feb. Similarly, my recollection is that indoor just wasn't as big of a focus for pros as it is today, but I could be wrong.