The same reason that yours, hers, his, ours, and theirs don’t have apostrophes.
Likewise, capitol and capital. The Capitol is located in nation’s capital, Washington, D.C. The dome of Georgia’s capitol, located in the capital, Atlanta, is gilded.
and the reason is …?
Because words like its, yours, his, hers, ours, and mine are all the basic word in question. An apostrophe is used to turn some word that isn’t inherently a possessive into one: Peter’s, Nemo’s, life’s, the universe’s, everything’s, etc.
“Bye-laws.” I know it’s British spelling but it just looks stupid.
“Paedophile.” This isn’t 1850; drop the snooty “ae”.
You’ll find interesting facts about that word in [post=7942272]this post[/post] and others in the thread, including that it’s a common pronunciation in Ireland and “highth” shows up in Paradise Lost.
You’re using the word “Reason” referring to the English Language? You might as well be using the word “Logic”. There is none and there ain’t no such relationship.