Why a noun clause cannot be the object of a preposition?

[edison_chen_e_c]

I've got to know the function of a noun clause in my junior high:

That he is homosexual is true. (subject)

All of us know that he is homosexual. (object of a verb) ('that' being a object is omissible)

There's no denying the fact that he's homosexual. (apposition of the noun 'fact')

etc.

I got a crucial conclusion: noun clause is not a clause but a noun. Here is the question, as nouns, why can noun clauses and infinitives not be a object of a preposition?

[Mister Micawber]

.
Some noun clauses certainly can: I know of what I speak. Let's go with what we know..

I can't think of any infinitives (bare or otherwise) that can be objects of prepositions-- but then, it is very late at night here now.
.
_________________
Canadian-American native speaker
who teaches English for a living at Mister Micawber's
ESL cafe: Interview with Mr. Micawber

[edison_chen_e_c]

It was in my morning, there's time zone problem.