The Titanfall games have been a victim of bad circumstances with their release each time- the original game found its potential curtailed by being restricted to the Xbox One (and so missing the more successful console, PS4), while the sequel, while releasing on all systems, was a victim of terrible timing, with EA releasing it right next to Battlefield 1, a titan game they put all their marketing support behind, while giving Titanfall 2 nothing.
However, it looks like in spite of all of that, the series has managed to find success anyway. Today, developer Respawn Entertainment and publisher EA announced that the series now has 20 million players, with Titanfall 2 having 1 million active players every month.
Now remember, 20 million players, or even 1 million active players, is not equivalent to sales- all player count means is the number of accounts that log into the game. Still, unless every Titanfall player has been making a dozen accounts, this at least tells us that the series has met some of the success that it deserves.