Not all trainers are equal - so why wouldn't owners send their best horses to Nicky Henderson and Willie Mullins?

In all sports there are always training trees. In football the managers of Arsenal and Chelsea learned their trade under Pep Guardiola at Manchester City. In American football many head coaches did their apprenticeship under the likes of Sean McVay of the LA Rams. 

In racing Dan Skelton was assistant to Paul Nicholls, as was Harry Derham, and Joe Tizzard rode for him. Ben Pauling, Jamie Snowden and Charlie Longsdon worked for Nicky Henderson. Gordon Elliott worked for Martin Pipe and Olly Murphy was assistant to Elliott. On the Flat the O'Brien boys watched dad Aidan in action all through their formative years. The list goes on and on. 

What that means is that training methods should evolve and get better with energetic, well-taught youngsters adding their modern twist to what the established coaches have taught them.