B/c when the fund managers buy assets to make the index fund to resell to retail investors, they usually get the same voting rights from their ownership as a normal shareholder, and they don't pass that part on to the retail investors, no?
Correct, Vanguard votes on the underlying assets of an index fund, not individual (or other) investors. You do get to vote if you own shares of individual companies.
It's not so much about that as an individual, but rather, is it good for the market that the managers of these index funds that just pass through ownership of the asset really get such powerful voting rights? To make it even weirder, I believe these funds are sometimes bought by public pension fund managers and the like. So it feels oddly corrupt.