Why would there be deflected agreement (the grammatical phenomenon found in Semitic languages) in the Book of Mormon?

Andrew C. Smith explains deflected agreement:

Deflected agreement is a technical term borrowed from the Arabic linguistics community that is also descriptive of a particular phenomenon in classical Hebrew. This term describes a grammatical principle generally referred to by Arab linguists as “feminine singular agreement with nonhuman plurals.” The basis of grammatical agreement in Semitic languages is that words from different categories or parts of speech (nouns, verbs, adjectives, etc.), when grammatically juxtaposed to one another, must agree in a number of details: number, gender, and, to a certain degree, definiteness. A type of DA, wherein parts of speech are grammatically juxtaposed but do not agree in number or gender, is also seen in biblical Hebrew, albeit more rarely. According to Gesenius’ Hebrew Grammar, “Plurals of names of animals or things, and of abstracts, whether they be masculine or feminine, are frequently construed with the feminine singular of the verbal predicate.
– Andrew C. Smith – Deflected Agreement in the Book of Mormon

Deflected agreement is found in the Bible and Andrew C. Smith has identified 329 instances in the original editions of the Book of Mormon which can be split into three types:

Verbal – nonhuman plural subjects with singular agreement expressed by the associated verbs
Pronominal – a plural antecedent is referenced using the singular pronoun “it” instead of the normative English pronouns “they” or “them”
Demonstrative – words used to distinguish certain entities from one another either spatially or in abstract senses within discourse

One example is found in 1 Nephi 15:3 which says:

For he truly spake many great things unto them, which was hard to be understood, save a man should inquire of the Lord. (emphasis added)

Why did Joseph Smith use deflected agreement while dictating the Book of Mormon? Why is the distribution of deflected agreement not standard across all the 15 books?

See:

Andrew C. Smith – Deflected Agreement in the Book of Mormon

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