They do that because they know human nature (well, post-popup windows from the '90s) is to move your mouse down to close the popup and then close the tab, as if it makes any difference. That buys them another 2-4 seconds of time-spent-on-page analytics metrics. It took me a bit to untrain myself from that behavior. I'd quite like a browser extension that stops reporting when my mouse moves out of the tab.
Here's the thing, why should I need to keep changing my behavior to stay head of the advertisers? On some websites I interact primarily through the keyboard, but on others I use the mouse because I'm doing a lot of scrolling highlighting.
