In a language, “HOW” explains the use of stressing the way the second part of a sentence functions.

He says

he likes

how kids are not being manipulated

into clicking buttons to buy stuff within this game itself.

The above can surely be written replacing “how” with that/the fact that but the first one is just concise and better way to present the same. Writing “how” (how) also explains that the author is curious of how such things happen.