There are quite a few questions floating around asking about earning/losing rep on per-site metas. Some of them are marked as duplicates to this question: https://meta.stackexchange.com/questions/91333/why-do-i-have-a-different-reputation-score-on-meta-stackoverflow-com-and-stackove which is removed for purposes of moderation. Others simply reference the per-site meta's help file which says:
Votes on meta do not affect your reputation; your meta reputation is the same as your reputation on Stack Overflow (synchronized hourly), though you earn separate badges. You must have 5 reputation to participate on meta.
In 2010, there was a blog post about the new spin-off per-site metas which says:
Reputation is always inherited from the parent site. You cannot gain or lose reputation* on the per-site meta. This also means that some reputation related functions like the rep graph and bounties are not enabled on the per-site meta.
*however, there is one exception: extreme misbehavior on the meta site will affect your parent site reputation. And not in, shall we say, the “good” way.
At best, this answer shares:
Everything drives from the parent site, which is at is should be. The meta site doesn't exist as a place to gain rep.
Nothing is really shared as to the philosophy behind WHY users should not gain rep on meta. Especially given the fact that rep exists to document quality participation.
Reputation is a rough measurement of how much the community trusts you
My question is more so the reason behind not gaining/losing rep on the parent site via per-site meta Qs/As and why it was decided to go that route when per-site metas were established.