Why isn’t this more popular?

Such a great plugin! Literally it will make your website seem like the fastest thing out there to the end user. It comes with a price, of course, you’ll end up with a lot of “pages visited” in your webserver logs that the client didn’t really visit, they were just preloaded in case the user clicked.
But overall it makes your website seem like it’s the fastest thing out there, clicking on other links etc on the page and they load straight away (tested for me with Chrome)
This is really a great add-on, along with a wp-cache plugin you’ll have the fastest site out there by miles.