Those have to be very good reasons, but they exist.
Seen twice this year: a process chain built on sh, java, perl, python, and two other "languages". There were several people that knew what the complete process was supposed to do, but none that knew all steps. The programmers that created the java and the python "chain-link" had left the company and none of the other developers knew how to change that code if it were broken. We decided to replace the functionality of the weak chain pieces with one of the languages that the remaining programmers were comfortable with. It was my luck they picked perl. Process chain back in working - and maintainable - order. I completely realize that if their knowledge of perl was close to zero and they picked python, that would have been as good a choice at this point in time.
Enjoy, Have FUN! H.Merijn