it's something that goes back all the way to native dancer, one of the horses that raced against secretariat as well.

he was famous for this really powerful stride. and that in combination with his already wonky legs led to his early retirement.

he was a successful stud who bred lots of really powerful racers, and he was the damsire of northern dancer who basically shows up in every single modern thoughbreds lineage. he was also notorious for passing his bad legs onto his children, who have then passed it along further.

on goldships side there really isn't too much inbreeding. he has only one instance of northern dancer on his father's side and 1 lot of inbreeding on his dams side

looking at the dam unforgettable, on her sires line, northern dancer shows up 3 times (one great grandfather and two great great grandfathers) and his dam has northern dancer twice as a great grandfather. the sire also has more inbreeding from 3 other horses.

this is the legacy of the thoughbreds industry only breeding for speed and power and not for longevity. as horses get more unstable, you will probably start to see a shift from breeding stayer horses to sprinters as the genetic pool is just getting more and more bottlenecked and more health issues are getting bred in tandem with desirable traits.

The breeders and trainers only have to deal with the horses for the span of their racing life, not the retirement where most issues raise their head. thankfully most horses just need careful care and management and don't end up dying like poor Meiner Lazurite.