HALO's story was done after HALO 3 as far as I am concerned. Who cares about the story of master chief these days? That shyt has been going on for 15 YEARS now...who cares outside of the diehard crowd?
That Halo 5 bundle was a fukking flop...turns out most have moved on from that same old narrative. Halo's strength has been multiplayer for 10+ years already.
Halo 5's "flop" could be attributed to a multitude of things.
For one, Bungie isn't behind Halo anymore and two, the SP from what I've heard was short and it was misleading. It's not even about the "story" but a good run through. MP is the bread and butter of Halo but there's definitely a healthy group that cares about the campaign of the series.
You can't just take it out because one game by a different dev wasn't well loved and think there won't be any backlash. Expectations weren't met with Halo 5 I'd guess. Plus, the SP in those games are MP enabled so essentially it's MP content since you can run through the levels with skulls and other players.
Still, being against a new mode in a game for what you perceive to be a Sp/MP only game is shortsighted imo. I'm sure nobody would argue that for example, a game like Uncharted 2 or TLOU "suffered" because they added multiplayer to the games. Hell, TLOU and UC's MP modes created a little online community that are now avid fans. To hell with the "This game should be this only!" mindset. Look what happened with SFV's reception and sales all because "but but MP only matters." Word of mouth damaged it.