I'm Right, But I Don't Know Why

“There is a lot of reasons to…”  Grammatically correct or not?  Discuss

Seems pretty obvious that it's not correct.  Why is this even a discussion?

It's not so much that I'm concerned with which whether this is correct or not.  Obviously, most people would "correctly" say "There ARE a lot of reasons to..." given that 'reasons' is a plural countable noun.  Therefore, the above statement would be considered grammatically incorrect...I'm just searching for the correct explanation as to WHY this is the way that it is.  Here's what I mean:

My issue stems from the grammatical differentiation between quantifiers and collective nouns.  The way I see it, "of reasons" could be considered a prepositional phrase, making the object of the sentence the singular collective noun "Lot" as in "There is a lot."  The addition of "of reasons" merely described the Lot, thus making the use of a singular predicate form "Is" correct.  This would be using the word "Lot" as a collective noun similar to talking about a flock of geese.  You would (correctly) say "There IS a flock of geese outside my window."  In that case, "Flock" is the singular object of the verb, therefore, the singular verb form "is" would be appropriate.  

All that said, the phrase "A lot of" is considered a part of speech called a "Quantifier," which when looking at sentence structure is a complete add-on.  In that case, the object of the predicate in the above example would be the plural noun "Reasons," making the proper verb form the plural "Are."  As in "There ARE reasons."  You add in the quantifier "a lot of" and you get "There are a lot of reasons..."  

I'm okay with this.  

What I'm not okay with is any explanation that's available for why a flock of geese is different from a lot of reasons.  Sure, there are grammar lesson websites on the internetz, and I've scoured a couple of them looking for a clear-cut answer, but I get nothing.  I more or less get "this is the way it is, so say it this way," and that's the end of it. 

My old statistics professor used to say, "People in most parts of the world speak broken English, except the United States where it's been ground into a fine powder."  I'm not always surprised because English can be really confusing sometimes.