A more than 2 year delay for the first game and never getting the rest of the series is a major downside for existing customers. That’s exactly the kind of monopolist behavior you are supposed to block mergers for. Waiting 2 years cost Microsoft a little revenue directly, but pushed XBox sales which was far more valuable.

Halo would have been a flop if it was Mac exclusive.

Keep in mind, this was back in the year ~2000. Mac market share in the home user market was a rounding error. Schools were full of iMacs, but at home, it was all Windows.

“Due out in the first half of 2000, Halo will have a simultaneous release for PC and Mac, with multiplayer compatibility between the two operating systems. While you'll need a 3D card and a powerful system to take full advantage of the game's features, it'll be scalable so you can play it on less powerful machines.” http://www.cnn.com/TECH/computing/9907/26/halo.idg/

Things got delayed ~18 months so Microsoft could port it to XBox thus waiting till November 2001. Then tacked on another 2 years to release it on Mac.