they would have to be completely deranged not to include multiplayer I mean I remember everyone buying it solely for the mp back then, many never even trying the single player.
To use a turn of phrase, they have a product for those people. It's called Modern Warfare 4's multiplayer. Remaking the campaigns for MW2 and also, rumour has it, MW3 is aimed at the sizeable demographic who love singleplayer, story-driven games. The developers never wanted the world's biggest singleplayer military FPS series to become dominated by MP fans the way it has.
One rumour (take it with a massive lump of salt) I saw claimed that MW4 is potentially the last traditional annualized CoD game. If it doesn't succeed, Activision are contemplating transitioning the series to a CoD Online GaaS affair. The rumour also claimed MW4 is a prequel to MW2 and a singleplayer demo will be released in April. So yea, grain of salt.
It's possible they're going to attempt to build hype for MW4's campaign by releasing the remaster/remakes of MW2 and MW3 before MW4 releases. The fact the remake has been rated in March is certainly worth noting.