First, I am certainly aware that language is dynamic and English, like all languages, has been constructed over time by usage and culture and hasn't been "engineered". English is what it is because language is dynamic and it evolves over time because of common use and cultural shifts.
How we express plurality has always been a funny observation for me. As an example, let's look at the word "meter". If something is a meter in length, we say "It is a meter long." No modifier is added. However, if we are talking about something larger or smaller than the unit, "meter" is pluralized and becomes "meters".
So far, this is basic English. Now, let's observe a couple of sentences without the plural suffix added to "meter".
He stands 1.8 meter tall.
There are 1,000 meter in a kilometer.
The box is .5 meter wide.
I walked a few meter.
This doesn't feel natural to the English speaker but the meaning of every sentence is easily understood. Plurality can be assumed by all contexts. So, my question is what's the purpose of modifying the original word if plurality can easily be discerned from contextual usage?
I am aware that English has derived from other ancient languages and, likely, this mechanism has carried over from earlier forms of language. Possibly, context might not have been so clear and modifying roots may have been necessary for clearer communication. If there is no need for plurality in our modern form of English, what was the context and nature of an ancestral language that established this mechanism?
I've studied a couple of languages, other than English, in my life. They've all had forms of plurality/singularity that is distinguishable by modifying the root word. However, none of those languages need the modification of the root word either. Plurality or singularity can be understood without it.
Why do we modify nouns to express plurality when it's simply not a necessary change to understand what's being communicated?