It has not lagged behind depending on how you look at it, video game development can be split into engine programming and gameplay programming. For engine programming, you only need a handful of senior engineers specializing in low level details of a video game engine, and these will get paid high appropriate wages that match industry standard salaries. For the gameplay programmers, they just seek the cheapest labor that can do "quantity over quality" type of work to pump out content and there's a large pool of juniors/interns that will accept these low wages just because they want to be a part of something popular.