In the old pulps, the mad science gadget was destroyed at the end of the story. If the hero kept it for later use, it either was one-of-a-kind and couldn't be duplicated or it was too dangerous to let the public in on it.
Silver Age Hawkman explicitly used ancient weapons because he didn't want Thanagarian tech to get into the hands of Earth people. Maybe this was official policy or maybe he just thought it would be like passing out hand grenades to a bunch of ten-year-olds.