Why do so many doors that request you to push actually have handles?

Axiom:
It is more cost-effective to manufacture, inventory and distribute a single version and have users under utilise those superfluous features versus creating 2 distinct versions.

Example:
It would be more costly to have multiple versions of doors for pushing and pulling. By creating one version manufacturing, inventory and distribution costs are reduced.
This is viable as under-utilising the product feature has a 0-cost for the user.