I think lots of folks who do reply fail to enable email notification of a reply. Then, with all the different topics etc to chose from when logging in they simply fail to arrive back at that topic.
Additionally, many times one poster will simply cover the ground in such a way that a second post would just be redundant. Except for the now devalued value of another link there is a pointless aspect to making a post.

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Electrical Contractor Resources. "You con du it with BURKEY BENDER conduit bender."
CONDUIT BENDER