Coronavirus origin could be bat, why this happen while people have been eating bats for centuries?
Bats are reservoirs of many important human pathogens, some are emerging infections (e.g., 2019-NCoV, the coronavirus in the news recently), and some are not (e.g., rabies). 

Contact between humans and bats is certainly not a new phenomena, but there is more required for an emerging infection than a reservoir and a new host. There must be some bridge that allows a virus to cross a previously effective species barrier. For SARS, there was an intervening amplifying host, the palm civet.  We've now had long enough to study the molecular biology, so this is now quite well described:


  Once SARS-CoV had jumped from bats to civets, it underwent further mutations in civets. The first K479N mutation allowed SARS-CoV to jump from civets to humans and the second S487T mutation allowed SARS-CoV to transmit from human to human, leading to the severe SARS outbreak in 2002–2003.


It may be useful to understand that, as they are RNA viruses, coronaviridae have a high error rate, increasing the rate of mutation. Additionally, making a species jump may allow for novel recombination.