It's clear that Metal Gear creator Hideo Kojima has a difficulty handing his series over to a team, disagreeing with their design decisions and not becoming directly involved with the project. This happened with Metal Gear Solid 3: Snake Eater and mostly recently, Metal Gear Solid: Peace Walker, according to a GamesCom 2009 interview with IGN.
"I always said that it [Metal Gear Solid 4] would be the last Metal Gear in which I would be deeply involved," said Kojima. "However, when we started the PSP version there was a lot of confusion within the team and it didn't proceed as I wanted it to. Therefore I thought that I needed to jump in and do Peace Walker."
There's another reason, too. Kojima Productions is currently upgrading its internal technology to develop console games -- Metal Gear Solid: Rising will be one of the first games employing this updated tech -- which Kojima needs to move forward on his next few projects. He figured Peace Walker could be developed before that was finished.
"This process is taking one to two years," he said. "However, within that timeframe we could do something, and we thought that because of this preparation period we just can't wait and do the preparation – we thought that within that timeframe we could do a PSP version."
Better get to work on that Zone of the Enders sequel, Kojima!