Due to their lack of funding for the development of Halo, Bungie originally sold themselves to Microsoft. Then, after Halo 2, Bungie wanted to stop working on the Halo series but was obligated by contract to continue creating games.
Following the completion of Reach, they purchased themselves back from Microsoft to begin work on Destiny, which they had been planning for some time.
They are now owned by Sony, so in addition to the company no longer wanting to produce Halo, a rival company also owns them. Reach personally didn’t appeal to me all that much, but I’m aware that opinion has since improved. Due to the fact that it wasn’t as bad as H4 and H5, many of its flaws are now simply overlooked by people.
Will Bungie ever get Halo back?
As you can see, things didn’t turn out the way they had hoped because they wanted to be their own bosses and work on their own projects.
Many Halo Bungie employees continued to work on Halo at 343; however, following the release of Halo 4, these former developers have begun leaving 343i. I believe that there are still two or three OGs employed by 343.