Since you said that nodes matter, I do think Bitcoin Core had been fair here by bypassing node voting since as far as I can see majority of nodes support/uses Bitcoin Core features. If they use it (letting node vote than miners) the possibility of Segwit being implemented is bigger than letting the miners to vote for the implementation. (That is if I understand it right)
I get this as Bitcoin Core believe that hardfork is not needed for the added update / upgrade for the Bitcoin features regarding scaling issue of Bitcoin. I also read that even with implementation of Segwit the onchain spam won't be solved is that true?
Yes, currently miners have every incentive to keep integrity to the bitcoin network - if bitcoin is attacked or changed, bitcoin price would plummet, bitcoin would not only lose uniqueness to other altcoins, but would also quickly turn those miners' business into bankruptcy.
Blocksize at 1mb keeps things secure and helps limit the onchain spam.
For anyone new or simply wanting to expand a bit more about bitcoin, I try to touch on a few of these points (and others) on post titled
"Hacks & puppets & forks - how to destroy bitcoin"
https://bitcointalk.org/index.php?topic=1834310.0