In both these cases we don't know exactly how transmission from bat to host ir from host to humans. SARS was connected to the food trade most likely but as far as I can tell we don't know if transmission to humans was due to a live animal sneezing, during slaughter or due to consuming an infected animal. In the case of MERS we don't even know if it is connected to the live food trade or merely from contact with sick camels.The virus can jump when the animal is killed or butchered.
Sometimes it jumps into a dead end. In other words, it can kill a different animal quickly which stops it in its track.
Unfortunately, this wee bugger found conditions just right when it made the leap.
Still a good idea to restrict wet markets and generally improve hygiene practices of course.