Allah decreed everything.... We can look through history and find particular things that may have aided in the lost of other schools... In general Allah decreed it all... It is interesting to look at the madhabs historically... What is interesting is that during the time of the Salaf, the first three generation, majority of the schools of fiqh, were Amal based, Shaykh Thawri, Layth etc.... I believe Abu Hanifa was the first hadith based madhab (strange that it is referred to Ahlul Rai by many Salafis).... The later madhabs were mainly hadith based all of them can trace their roots back to Abu Hanifa and the influence of his students on hadith... And all the Amal based madhabs died out accept Malik's school, due to his strong students... Which is why I believe Malik's madhab is actually closer to the truth... than the other madhabs... because of it resembled practice of the Salaf... I say this as a Shafi..... I think hadith is actually weaker than amal... the problem with amal it is difficult to prove........ which is why people later generations preferred hadith based madhabs... I think.... And Allah knows best...