So they had ".com" = corporations/companies, ".org" = non-profit organisation, and ".edu" for the educational research groups, ".mil" for the military", and ".net" for the companies that managed the continent wide networks built from fibre-optics and satellite communications.
.com is derived from the word "commerical" which includes but is not limited to corporations and companies.
Back in 1985 when .net was created I don't think there was "continent wide networks built from fibre-optics". .net was intended for network technology companies, ISPs (local, national and international) and infrastructure companies. Although, no restrictions were put on it's use so it has become a general purpose name.