Anybody that thought Titanfall would have longevity is
delusional. That game obviously from day 1 wasn't going to have long legs because all it focused on was the novelty of "titans falling on the ground OMG!!!" which got OLD very fast. Yea it's obviously people here and there playing it from time to time but come on it's not on the level of a game like say Battlefield 4 which is still getting HEAVY burn by people right now.
After that you're left with a meager 3-4 playlists that's pretty much all the same and no differentiating content. Titanfall proved that "fun gameplay" alone wasn't going to carry a game forever. COD/Halo at least thrived because it had like damn near a thousand playlists with actual co-op so there was something for everyone. Titanfall was all "shoot people and press down to bring out a big ass robot!!".

"Oh here's some robot a.i. from the cloud to shoot at."
Titanfall was the fastest MP game I've dropped in a long time. Even halo 4 got more burn than it.
Destiny on the other hand not only has amazing gameplay, it's chock full of content. I mean you have huge worlds with missions, strikes and exploration to do with partners online with an actual story component and then you have PVP which is great too. There's literally too much to do in Destiny.