"why would they draft the manifesto you claim does not adhere to its spirit while its very authors claim otherwise?"

Because the Scrum guys were only two of the 17 who created the Manifesto (which is only the four values).

Just because those two guys were in the group that created the Manifesto does not mean that it is what they would have preferred it to be. By agreeing to it, they obtained a fantastic marketing tool for promoting Scrum, which IMO is not consistent with the Manifesto.