Mainly it was because of the deep religion impact on society and individuals. The church had become the most powerful institution during the middle ages, even surpassing the power of the kings and nobles.
Anything rational or scientific said against the established religious teachings were regarded as Blasphemy and those who did that were severely punished. Even killed sometimes.
According to Buddhism, when people were finally free from all earthly concerns, they would reach nirvana. ... Buddhists believe that worshipping the Buddha helps them follow the Eightfold Path. for the first time, these groups heard that they, too, could reach enlightenment.