"Ya, sure!! but keep it with your friends because the more words this language has, the more harder for this language to be taught to other people who dont speak this language."

I don't have a problem. You clearly do. "the more harder"

Why should the fact that no one person knows every word in the English language mean that we shouldn't create new words?

When a word describes something we no longer use (e.g. phonograph), or is superseded by a new word describing the same thing (e.g. piano for pianoforte), or is now considered discriminatory (e.g. fireman), it begins to fade from the popular memory. There is little need for an English speaker to know all these obsolete words.

There are also jargon in many academic disciplines which laypeople do not need to learn. Does everyone need to know what a prokaryote is or what the optative mood is? Of course, it doesn't hurt to learn them, but who can learn them all in one human lifetime?

Now, as new technologies are invented, new discoveries are made, new theories are proposed, we need to be able to describe them all. In some cases, a new word is the best way to do it. Do you want to watch "television", or watch "electronic device that displays moving images on a flat surface"? Do you want to call WoW an MMORPG, or call it an "electronic game played with many people at once all pretending to be characters who kill monsters"?

The language evolves to cater for the times. As long as society changes, language will change along with it.