It's entirely possible that an FTC employee or some politician was screwed over especially badly by one of these corpo vet offices and decided to make it a personal mission. People love their pets.
That's completely made-up! It's possible someone had a bad date with a PE executive; it's possible they are susceptible to sunstroke, spent too much time outside on a summer day, were a little woozy, and approved something that they otherwise wouldn't. Maybe they were going after PE for something else, but that fell through and they limited it to vet clinics. We can go on forever! Or maybe, they discovered a violation by the PE-owned clinics and did their job by acting on it.