I've been told that the translation of the following sentence:
100年以上続く古い会社なんで不便もたまにあります
is: This company has been established for more than 100 years, so it is sometimes inconvenient with many things.
I understand both parts of the sentence, but I don't get the connection なんで. Not even in the dictionary says that なんで's meaning is "so". The only meaning of なんで I know is "why?" but here it makes no sense.
Thank you