Why do people feel it necessary to add “of” to some phrases?

@HS there is some discussion on this topic here:

http://www.antimoon.com/forum/t11916.htm

the last two comments there attempt to distinguish the meaning of "not much choice" from "not much of a choice".

Certainly both phrases with or without "of" are in use.
If one searches the web for "that big of a deal" and similar phrases, their usage seems to have taken off in print since the 1980s, seemingly on both sides of the Atlantic. Whether this is because the "of" was edited out prior to that is not clear.

I will be honest and say that I have no academic background in the use of words, grammar or punctuation, that is aside from a high school diploma that I barely acquired in my youth. In fact, in almost everything that I have typed, am typing and will type, it will be quite understandable if one was to find a multiple amount of errors. I have probably proven this within the few sentences that I have written here. However, this does not stop me from trying, nor does it stop me from learning. I love to learn about words, their history and their origins. Before I research, when I come across a word that I do not know I first guess at it's story and then search it out. So allow me to try that here with the word 'of'

Now I could be completely wrong or I could be on to something. When I think of 'of', I think of it in relation to a subject or topic. When we say "How bad of a decision" the of refers to the particular decision. If we were to say "How bad a decision" there is more ambiguity as to what decision is being referenced. "How bad a decision?" could be any decision, whereas "How bad of a decision?" is more specific to the situation at hand. "A decision" is more abstract and free. "'Of' a decision" is a little more concrete and belonging to. Call me crazy or just plain wrong, but hey I got to play in the world of words for but a few moments.