Okay, so ever since the transition from Bungie to 343, I knew that there would be a Halo 4-6. It was somewhat blatant. Bungie obviously is associated with 343, easily noticed for TWO reasons.
7 is the cubed root of 343 (7x7x7) EASY. A cubed root is a number times itself three time. Two studios make the two trilogies. SIMPLE.
The other reason is the most obvious reason… 343 Guilty Spark! What about the oracle? And it just so happens that after you destroy him, the game rights are sold to who other than 343 industries!