Manners are in fact detailed prescriptive means & methods for being submissive, or rather for sending submissive signals, as the default behavior in societies where there are more humans living together than normal, i.e. anytime after 1800 when the population really started to shoot upward and to urbanize. It ends up being very practical to train people to be submissive in an urban industrial society, because if you have a thousand supposed self-declared alpha-apes constantly fighting it out "out there," things become a mess very quickly.

Edit: to the respondents, I am intentionally keeping morality out of it (decency and so forth), because a strictly moralistic right/wrong judgment-based view didn't seem to be enhancing the parent's understanding. But dominance & submission, like morality, is just another narrow rubric for viewing the world, doesn't describe the whole world, and isn't the only way of describing the world. So it's best not to take it too far beyond a blurry big-picture view!

However fawning and currying favor may indeed be submissive, but are not proscribed by any idea of "politeness" I am aware of. Excessive accommodation to the detriment of yourself and your interests would also be submissive in my view.

I disagree, I think it is more submissive than doing the opposite. But that's not a bad thing - people who are never submissive don't fit into society. They have terrible manners and drive dangerously, like you point out.

A certain amount of strength is admired, but too much and you're almost unilaterally rejected.

But some people might be so submissive by nature that "Never Submit" is good advice for them, because in those situations where they really should submit it will never even occur to them not to.

The manners you speak of are the hypocritical sort - e.g. calling Trump "Mr. President" even though he deserves no respect in any sort of situation, just because he is "the President". It is this sort of manners where people (i.e. the talking chimpanzees) get upset because social protocols are being violated - the social protocols used to enforce submission, dominance, and status. These social protocols are used to cover up all the bullshit talking chimpanzees like to get up to.

Someone who is almost always selfish may find they are the most respected when they accomodate.

A lot of timid people are attracted to strong people. You say the things they wish they had the bravery to say, and they respect it. It's aspirational.