Digital cameras in the 70s and 80s were impractical, low quality devices that were mostly useless without a computer, which is not something that the majority of people had in their homes.

Kodak did follow up with digital though. They had a digital SLR by 1994 (before Canon or Nikon) and digital cameras for $299 by 1996.

The advantage that companies like Nikon and Canon had are their lenses, and the huge investments photographers made in their lenses is what locked them in to a particular brand.

This is why a lot of traditional camera companies (Konica, Minolta, Fuji, Polaroid) were unable to keep up.