Why is 'Who determines who will be hearing' thus?
Because "determining" is volition/intention as the will in action as a verb. You just referred to hearing (the noun) as hearing (the verb), presuming hearing is an action that accomplishes something. That's the quandry you're in. That's why you can't understand. Because of English construction, your heart and mind is patterned to process such nouns as verbs. You can't get away from it. It's your fundamental epistemological default.
You keep processing nouns as verbs, insisting man can effect his own salvation; but then denying that it's a work. Faith (belief) is not a work; but believing (faith-ing) IS a work. By saying that any man believes and is saved, it means that man has accomplished his own salvation.
Faith is a noun. It isn't doing. One must have faith TO do anything as believing. That faith comes from hearing, which is also a noun. It's not the action of hearing. Hearing doesn't save. Any action associated with, or subsequent to, hearing doesn't save.
The thing heard and the thing believed saves. That's the Rhema of God, and it's by God's grace and the faith that He gives.
You certainly don't consider man able to hear.
The verb again. This is the hugest obstacle for Modernism-sculpted English thinkers/speakers. You can't even think or speak about the noun. It's always the verb. And that's because you presume man can save himself by believing. The belief/faith that comes out of the thing heard is the Word (Rhema) of God flowing forth.
Rhema is Rheo- and -ma. Rheo- is both to flow and to speak; and -ma is the Greek suffix that always represents "the result of". Rhema is the resulting flowing of speaking as a noun. And it's anarthrous, not articular.
It takes a bit to understand that, and one has to be willing instead of clinging to a presupposed disposition by one's own conceptualization in English. Englishizers have NO grid whatsoever for Greek anarthrous nouns, and instead have something ELSE in their place. It's a double whammy.
Who else. then, made it happen?
Again looking for a verb. The anarthrous Rhema refers to latent qualitative functionality that is NOT a verb, but is activity.
For instance, a table that is holding up several items is simply exhibiting its anarthrous qualities as a noun by "doing" that. It's an activity related to the nature and design of its "tableness". A table is never "tabling" to hold up a lamp or book or candles or whatever. It's a noun. But there is a latent functional activity for that table that includes its designed purpose.
God's Word, hearing, and faith (and ALL Greek nouns) each have that anarthrous form. English can only use adjectives and endless employment of semantics to provide some translational equivalent, because this is a structural inequity between donor and receptor languages.
The faith (noun) that flows forth from God has the latent functionality within itself. Faith "does" it, but it's not a "doing" as a verb.
But the righteousness that is by faith says: “Do not say in your heart, ‘Who will ascend into heaven?’ ” (that is, to bring Christ down) “or ‘Who will descend into the deep?’ ” (that is, to bring Christ up from the dead). But what does it say? “The word is near you; it is in your mouth and in your heart,” that is, the message concerning faith that we proclaim: If you declare with your mouth, “Jesus is Lord,” and believe in your heart that God raised him from the dead, you will be saved.
"And I, when I am lifted up from the earth, will draw all people to myself."
Go back and read what I've delineated if you really want to understand. Calvinists need to do so, too.