What we DO know about inbreeding is this: for example when the rich in Europe only married out their children to the rich, to keep the wealth in the family, they ended up having to marry off children so closely related their offspring was infertile or in worst cases mentally ill.
What we know about the Akhal-Teke breed and it's small start up population is this: we are the ONLY breed that has the Naked foal Syndrome. With NFS testing and working with VNIIK we now know the common ancestor who passes this deadly gene on.
Meet 685 Angar, a stalion born in Ashgabad in 1959.
Breed a sire to a mare whom are both affected and you have a high chance a foal will be born that will suffer a miserable death.
Why do people inbreed? In the USA most cases are ignorance and lack of dedicated breeders who understand the downfall of inbreeding. Lack of available stallions in the USA 20 years ago...In Russia....money perhaps? Since government run farms got privatized and farms struggled to make income?
Would you happily marry your daughter to your cousin?...well...you know the answer....why do it to your horse!