The foundation of the business has shifted from sport to sales. The market wants fast, precocious 2-year-olds who will win early and back up their pedigree as quickly as possible to minimize the risk and overhead. Horses are running faster now but racing far less frequently and at shorter distances. They are also being retired to stud/broodmare duty much earlier in their careers, most before they ever sniff their prime.
Many think the focus on speed over stamina has been detrimental to the soundness of modern TBs. And yes, bloodlines are being diluted by overbreeding stallions. Some also feel the prevalence of medication like Lasix has adverse genetic effects.
Thanks for your answer. (I haven't kept up with the sport.)