Speaking during Microsoft's Build 2016 conference, Spencer indicated that Halo 5, specifically, wasn't likely to be released for the PC, but left the door open for future titles.
"Halo 5 was shipped as a console game," he said. "If we're going to [bring Halo to PC] moving forward then we're going to plan on both platforms.
"I don't want to get into the world where we're looking back... it doesn't mean there's nothing [in Halo 5] that could ever end up on PC, but I'd much rather look forward with what our plans are."
Elsewhere during the Q&A session, as reported by PC Gamer, Spencer outlined Microsoft's strategy in bringing Xbox One games to PC and vice versa. He noted that a game's suitability for each platform was a major factor, not just whether it supports controller or keyboard and mouse.
"If I enable keyboard and mouse on a console, which we will do, and then you download [real-time strategy title, Ashes of the Singularity] and you're playing on a monitor, is that a PC game or a console game? I get out of saying 'all,' because I think there are games that people want to play in front of their monitor with a keyboard and mouse, and I want to be somebody that builds those games."
He added: "You should expect [releases on both Xbox One and PC] when franchises look like they belong on both platforms, but I wouldn't go so far as to say it's a mandate for the studios because it's not."
Microsoft previously confirmed that Forza 6 Apex was just the first entry in the racing series to come to PC. Turn 10 creative director, Dan Greenawalt, revealed the company plans to release all future Forza games for both Xbox and PC.
Apex, meanwhile, is a free-to-play version of Forza 6. It is due out later this spring, though a release date has not been announced. Another Forza game has also been announced and will likely be fully unveiled at E3 2016.
Killer Instinct, which was first released on Xbox One in November 2013, made its PC debut on March 29. It is available now on Windows 10 through the Windows Store. You can check out the game's minimum and recommend PC requirements here.