Probably because WikiSuccessCanInhibitNewWriters, new posters often begin with a bit of a tirade. The WikiMaster gently turns this positive rather than responding directly.
I've experienced a few of these myself; I often reread what I wrote later and, while still thinking some of my points as valid, I wonder why I needed to express them so forcefully, and why pique tends to creep into them. Some of this I can definitely trace to my own personality, but some of it also seems to be encouraged by the Wiki format itself...It is very easy to create and name a Wiki page that offers a simple, singular concept or statement, especially one that is polarizing, an extreme position. The problem is that very little in the real world is so simple. It is much harder to conceive Wiki pages that are more carefully worded, to present concepts that only apply some of the time or in certain cases, or that describe tendencies or possibilities or contributing factors. Perhaps there is a tendency towards WikiPolarization.
I think that the main things that upsets newcomers, is the way that they are treated and the way that all this nonsense of OffTopic and OnTopic is handled. There seems to be those EditVultures?, DeleteVultures?, and plain old cranky WarLords? that are looking to force their will upon others by assuming editorial control over everything new they create (or even deleting all their pages). By treating newcomers more gently, and taking them under wing, wiki can be a much better and peaceful experience for all. It would be prudent to place the WikiExperience tag in all situations that are starting to boil.
See: WikiExperienceCategoryWikiTag | CategoryWikiLife?