How did “as” amass all its confusing “broad and vague meanings”?

Question

From Bahrych, Merino. Legal Writing and Analysis in a Nutshell 5th edition (2017). 343:

as. Do not use the conjunction as when you mean “since,” “because,” “when,” or “while.” Its broad and vague meanings can create confusion. For example, As a potential work stoppage threatened to block the opening of school, the arbitrators revised the wording of the contract. Does as mean “when,” “because,” or “while”?

https://www.etymonline.com/search?q=as doesn't answer my question. Incontrovertibly,

“since,” “because,” “when,” or “while”

are NOT completely synonymous. For example "since" can mean "because", but "because" can't mean "since".

More Examples. General Electric is the only company that has retained its place on the DJIA under its original name since because the index's inception. When While did you last get your teeth cleaned?

Answer 1

OED:

As adv. & conj.

Origin: A variant or alteration of another lexical item. Etymon: also adv.

Etymology: Originally the same word as also adv., now distinguished in form in the senses below.

The current form of the headword is the result of the progressive phonetic reduction of Old English eall swa , which originated as an intensification of so adv. and conj. (see also adv. and compare Germanic parallels cited at that entry). This intensive formation was used in Old English in all of the main historical senses of so adv. and conj., appearing in correlative constructions expressing comparison of equivalence, most commonly as an antecedent adverb in a main clause (e.g. eallswa beorht swa gold : compare sense A.) but also as a relative conjunction in the subordinate clause (e.g. eallswa beorht eallswa gold : compare sense B.), and outside such constructions as a simple uncorrelated demonstrative adverb (see Old English examples at also adv.).