How did s become a plural in English?

I am sure you would have wondered even as a child why the letter ‘s’ came to denote the plural form for majority of the words in English language. I was recently trying to research this information and came across this article which said, “The invaders oversimplified the Old English by simply adding –s to a singular noun to make it plural”. And this article hypothesizes that the old English had nominative case plural words like hundas for dogs ending with ‘s’, this led to over-simplification and modern English getting most of the plural forms with the magical addition of the letter ‘s’. However, none of them mentioned why the letter ‘s’.

Well, here is my hypothesis on why the letter ‘s’ specifically came about to be used for plural forms(and why not other letters). In Sanskrit(oldest language of the world and also known as the mother of all languages), we take the root word(praatipadikam), add the corresponding suffix(pratyaya) for the corresponding case and get the resulting word. Sup pratyayas(सुप् प्रत्ययाः) which are used to form the different cases of words like nominative, accusative, dative etc. have the ending s(स्) for most of the plural forms . For example, we are considering a word baalaka(बालक meaning boy). jas(जस्) is the sup pratyaya for the plural of nominative case: baalaka+ jas (बालक​ + जस् ), ja disappears due to a rule(sutra-one of the many grammatical rules of Maharshi Paanini) ending with baalaka+ as = baalakaas(बालक​ + अस् = बालकास्). Later the ‘s’ becomes visarga( ः) due to another rule making the final plural form baalakaah(बालकाः). But the important point here is that baalaka first became baalakaas which is how we see the words are made into plural in the present day English language.