There seems to be two reasons for this:
1. The 'authorities' on this topic, in all these forums, will tell men that there is a risk in getting a hair transplant regardless of who you go to. So with that logic, why spend a large amount of money if you cannot even eliminate the risk of the transplant going poorly? For example, if I had a transplant with HW and it went poorly, I would be advising as many guys as possible that there is probably no difference between western and Turkey clinics (to an extent).
2. There seems to be an consensus going around, while maybe uninformed, that western hair transplant doctors specialize more in transplants for 50+ men with a lot of money who just want some coverage on the top of their head. While in Turkey they are more attentive to the needs of younger guys, who actually need proper hair. I'm not saying its good practice for the long term, but it is what it is. The results galleries of these clinics somewhat reflect this, and combined with the price difference, its no wonder they flock to Turkey. In the minds of a lot of men - an unnatural hairline > a natural receding hairline.