The change should reach your devices sometime in the next week.

Facebook didn't explicitly outline the reasons behind the decision, but it has ongoing plans to make Messenger faster and lighter rather than an a do-it-all front end. The decision to axe Discover certainly helps achieve that goal. It's also an acknowledgment that all-encompassing apps like WeChat and Gojek might fare well in places such as China and Indonesia, but don't get much traction in North America and Europe.

There's also a financial incentive. Now that Facebook displays ads in Stories, it's not so dependent on the Discover tab to profit from Messenger. It might rake in more cash simply by encouraging people to check their Stories more often -- other businesses probably won't like it, but Facebook clearly sees it as an acceptable tradeoff.