Depends on the company I’m keeping, I had an Aunt once who, when I was reading a part of my thesis asked me how I knew all those big words and why she had never heard me speak like that? I told her if I spoke like that around her she would never understand what I was saying, she was quite insulted. ?

The English language is incredibly versatile and nuanced. Often words with similar meanings can convey completely different ideas in different contexts. On a separate note, I hate to repeat words when it's not necessary.

It is boring to read a paragraph that uses a word again and again.

Sometimes The right word conveys volumes. However when I see 5 paragraphs of them, I think the writer has very little to say and/or very little confidence in what they are saying, and are trying to baffle me with BS.
I usually say so, in just a few words...just call me Ms. Popularity, LOL!

Because i, and a lot of other folks, just really like words.

Because some of us actually read, write, and converse at a much higher level and have no need to "dumb down" our communication as we generally avoid interacting with idiots.

There are occasions where EACH is appropriate. I love the flexibility of English.

I agree with @Darius77 It’s fine to be “plain spoken,” which means to use simple language, but a larger vocabulary permits more nuance. For example, it is correct to say “Donald Trump is an idiot,” but it is more accurate to say, “Donald Trump is asinine,” which means he is extremely stupid or foolish. ?

Bombastic is a good Scrabble word but you have to have the right set up to play it because it has 9 letters.

Because there are no two words in the English vocabulary that completely overlap. There are only near synonyms, which can be used to communicate the subtleties of one's intended message. That's how wordsmiths come to be:

I take most imperious unbrage with your bellicose assailing of my right to use big, scary words if I wanna.

I am dumbfounded, nay flabbergasted that one would strive to impugn the use of grandiose loquacity merely for its ostentatious essence. I find that to be needlessly prohibitive and an assault of one's liberty of phraseology!

From James Earl Jones.
"We are as humans gifted with the use of language.
we should intend to use that gift to the fullest".

It is to make it more interesting and lively.....! Why confine ourselves to just a few when we have thousands to choose from? It would be like living on bread and water when there is a whole array of foodstuffs just waiting to excite our palates.

They like to appear clever