Is it morally wrong to "want" the market to crash?

It's a zero sum situation. Some people win means other people will lose. And vice versa. I think the only immoral thing to do is to inflate prices of essentials like house prices, foods, and loosely regulated assets like crypto currencies, plots of useless land sold at high prices for potential gains which will never materialise, etc. The rest is fair game depending on skills, knowledge, luck.

I think it's less that people want a crash to happen but more that they believe it's inevitable, and thus, want to take advantage of it.

Their existing investments and job security may probably be affected as well.

And because they fear buying high, they'll wait for markets to drop.