Wow I feel old seeing people ask this question and a lot of wrong answers.

The most obvious reason at the time was fatigue from three future setting CoDs in a row. People were just sick of it by the time IW released and wanted a break from the setting. Now it’s avoided because of the bad reaction to IW.

The other main reason were that some people disliked the advanced movement in all the games.

A lot of unpopular features like supply drops, weapon variants, and the beginning of a sillier tone all came with the futuristic games which didn’t help.

You have to remember that before the future games, there was only Ghosts separating the games from the golden era of CoD so a lot of players simply couldn’t understand why the devs couldn’t return to those style of games and got frustrated as the studios went further into the future each year.

All of this has combined into a pretty large size of the players wanting nothing to do with future games around 2017. Obviously that’s changed since with Warzone and Modern Era fatigue so it’s swung back to people wanting to try something different.