Why isn't block header signal considered voting?
Because Bitcoin is not ruled by miners:
https://en.bitcoin.it/wiki/Bitcoin_is_not_ruled_by_minersAlso read Harmony and Discord:
https://bitcointalk.org/dec/p1.htmlThere are many groups. There are miners, there are users, there are developers, there are traders. All people using Bitcoin form a consensus. Signalling is not voting, just because not only miners decide, what is and what is not Bitcoin. If Bitcoin would be ruled by miners, then they could decide to for example get all coins and ignore all signatures. Or to increase block reward to 100 BTC ad infinitum. But they cannot. They could start signalling for such changes, but because signalling is not voting, those rules can be still rejected by non-miners. That's also the reason, why full nodes are so important.