Will he stay?

Orchestra has.

Probably for the same reason that my longest bicycle training ride was 130km when I was training for my first 200km sportive.
You don't want to leave your best performance on the training grounds.  And horses need to kept interested, not over-stressed.

My mate trained for a marathon by doing short (relative) sprint distances. The best way to improve fitness is getting the heart rate up and going fast. When you then go at a slower pace it is easier to get the longer distance.