It’s not that TB racehorses are never lunged ever, it’s that per your original question, expecting to be able to lunge one on the backside is unrealistic and not going to happen.
TB race training can vary greatly depending on the stable and its resources. Some actually have a very “traditional” breaking with groundwork/round penning, lunging and long lining, hacking in the woods, even some very rudimentary dressage. Some don’t get that at all and more or less all they know is riding on the track.
While I was in Virginia, I managed/trained a string of hunt horses and filled in helping at the racing stable that shared the property. We mostly had steeplechasers (one or two that flat raced), and they got a very comprehensive start and training regimen complete with dressage and gymnastic schools. We did the majority of their training/conditioning at home on VA hunt country. What I saw of that area, most steeplechasers had pretty long careers and retired with their owners or found a second career in the hunt field. There wasn’t a need in that area (that I observed) for a CANTER-like program for steeplechasers. Can’t speak for anywhere else and that was 10 years ago.