According to Ryan Payton, who worked at Kojipro at the time, MGS4 was ruinning on a Xbox360 dev kit and staff + Konami wanted the game to release on it, Kojima refused
The Rumor That Won't Die: MGS4 semi-confirmed for Xbox 360? - Siliconera
MGS4 25th Anniversary Edition' for Xbox 360? Not so fast, says Konami
Amazon.com: Metal Gear Solid 4: Guns of the Patriots : Video Games
Metal Gear Solid 4: What 360 owners dream about | Next-gen console // pswi60
Metal Gear Solid 4: perché non è arrivato su Xbox? - NerdPool
MGS4 For Xbox360 (@MGS4MGS1Xbox360) / Twitter
Metal Gear Solid: The Legacy Collection won't come to Xbox 360 due to MGS4 | VG247
Amazon.com: Metal Gear Solid V: Ground Zeroes - Xbox 360 Standard Edition : Konami of America: Everything Else
Metal Gear Solid 4 coming to Xbox 360? The rumors are baaaaack! – Destructoid
Amazon.com: Metal Gear Solid V: The Phantom Pain - Xbox 360 : Konami of America: Video Games
Metal Gear Solid 4 is (mostly) a masterpiece - so why is it so hard to play? - GamesReviews.com
Amazon.com: Metal Gear Solid HD Collection : Konami of America: Everything Else