I'm pretty sure most employees at 343 played Halo even before being hired and I'm almost certain they played all the games during development of Halo 4. Hell they probably had regular matches of CE or played through the campaign during CEA no?
Heck, a while back, I remember reading something on Quinn's twitter of Ellis playing like over 8000+ games of Halo 2.
It's not about that. They simply didn't want to make Halo CE 2, they wanted to make Halo 4, they wanted to build off Reach and incorporate staples of current FPS like Call of Duty etc.
In the end, it just wasn't fun and didn't work. And I'm pretty hopeful for Halo 5. Not because I think they'll capture the magic of CE-3 or whatever, but because it'll be better than Reach and 4 and be a solid arena shooter in a landscape full of ADS shooters like Destiny, CoD, TitanFall
Maybe they were testing CE and how it plays for a possible re-release or a release on Steam, seeing if it's still fun or just for the fun of it.