All's fair to keep users for as long as possible inside Messenger and, after the bots, Facebook is deploying something that may do the trick: games... instant games
These Messenger Instant Games are HTML5 games that can be played instantly in Messenger requiring no additional installations or lengthy downloads, and bet on the multiplayer component to ensure a healthy dose of competitive fair play to make us want to play "just one more time".
In fact, Facebook is well aware that these games are not intended to replace native games, and that's why the focus is in very short gaming sessions, roughly 30 seconds each, so you can play it whenever you have just a spare moment to spend. But do not think that these keep them from being quite interesting and engaging. Besides classics like Space Invaders and Galaga, there are games like EverWing (among others) that will surprise you with the quality that can be achieved in an HTML5 game - and I'm sure there will be countless other pushing the envelope of what HTML5 gaming can provide.
Sadly, Facebook has once again decided to launch just in a select number of countries (Norway, Denmark, Switzerland, Sweden, Great Britain, Canada, United States, Japan, Netherlands, Australia, Austria, Latvia, Germany, Ireland, Belgium, New Zealand, France, Singapore, Finland, Hong Kong, Russian Federation, Estonia, Taiwan, Slovenia, Puerto Rico, Cyprus, Israel, Lithuania, Spain, and Italy) - leaving Portugal out of the list. I sincerely can't understand why, in this "global" world, they don't allow anyone/everyone access the same content wherever they may be!