How does a business get money from investors?

What you're describing is a scenario in which John sells 10% of the shares that he owns to someone else. This is analogous to you buying META stock from someone else through a stock exchange. You are correct that the company never sees any of this money.

What you are really trying to understand is when a company issues additional shares to raise more money for itself.

So a more accurate description is: suppose WRU had issued 900 shares, and John owns them all. In order to build a factory, it issues (with permission from the Board of Directors and existing shareholders) an additional 100 shares for $1 Million ($10K per share). The money from that sale goes to the company's accounts, not John's.

John's 900 shares are now "worth" $9 Million, but represents 90% of the company instead of 100%. His percentage is diluted but his value is not, since the company gets the money from the sale, which increases (all else being equal) the value of the company proportionally.

I use "worth" in quotes because that presumes that someone else is willing to buy all of his shares for the same price. Until then, the value (and the gain for tax purposes) is completely un-realized.