Halo Wars 2, for those who don't remember, was originally released back in 2017, and despite seeing some success didn't become the hit people expected, struggling to carve a niche in a crowded RTS market. Aimed more at console and casual RTS players, who may be more fans of the Halo universe then they are of the genre, it struggled to maintain a strong player base. 

343 did roll out updates through 2017 that improved the game somewhat, but the game was dead by the time 2018 rolled around, and has been abandoned ever since, even following a petition in 2019 for the studio to resume support for the game. 343 have now gone on record however to state this won't be happening, and that supporting the game "just [isn't] possible."

Originally, studio explained that the team who are working on Master Chief Collection for PC were the same team behind Halo Wars 2, and that the level of work put into that release made supporting Halo Wars 2 impossible. Further, while they don't rule out a possible return in the future, the team is "unable to commit" for the foreseeable future. But even with the release of MCC now done and dusted, the team are still not planning a return to Halo Wars 2.

"We always strive to be open, honest, and transparent with our community and we know many of you have been waiting, asking, and hoping for news about the future of Halo Wars 2," the studio said in an update. "We want to acknowledge that we’ve heard you and make sure you know that this feedback and these topics do indeed get brought to the right folks across the studio for further evaluation." 

In the past, we’ve noted the Publishing Team was fully focused on MCC and we had no current plans to return to Halo Wars 2. Now, with all the titles on PC, we’ve seen these questions popping up again although the 343 Publishing Team is still working on more MCC seasonal content along with a variety of features and further improvements. It’s not always easy to be open and transparent—particularly when we expect it’s not an answer the community wants to hear—but we want to give it to you straight: 343 Industries has no current plans for further Halo Wars 2 work including content updates, balance patches, bringing the title to other platforms, or a new game in the series.

So it seems that, while the phrase "current plans" may still leave a door open, 343 have no intention to ever return to the game. It seems the studio consider that it's time and resources are better spent elsewhere.