Halo could become even bigger with Steven Spielberg doing a TV series.
It is one of the very rare franchises that really offers something fans can't wait for. I want to see the sequel to Halo 4, because I want to know how the story continues and what is next for Masterchief.
The games you mentioned can't deliver on that front... Story driven games are very rare these days. Metal Gear, Halo, Quantum Break and maybe a handful of others. Besides those games there are not that much Next gen games that are story driven. I am not saying they have to be though.
Titanfall, Mario, Zelda etc. will work without a deep storyline. Halo is just one of the VERY rare games that has it all. Singleplayer, Multiplayer, great sound, great visuals, great story, map-editor etc.
It is one of a kind.
I am actually looking forward to CoD Ghosts, because they made it pretty clear that this is the way they want to go.
Imagine not having GamePass on your console...