However, the reasons why we are asked for our credentials such as MA, BA or the teaching certs for these kinda jobs are quite puzzling aren't they?

My understanding is that foreign teachers in China require a "foreign experts' certificate" in order to obtain a work visa. The certificate is issued by the local provincial education department, and is normally issued only to foreigners holding at least a three-year Bachelor's degree. Unlike you, I'm not puzzled. Maybe you aren't now.