What's up is how much the game has changed over the years. Rule changes in recent years have helped open up the passing game. For example, in 1978 the NFL freed up receivers by restricting contact beyond 5 yards downfield. At the same time, it permitted offensive linemen to extend their arms and open their hands on pass plays. To give a sense of the impact of the changes, consider that in 1977 the average number of passing yards per game equaled approximately 284 yards per game. By 1980, it climbed to 392! And more changes were implemented in 1994 that helped the passing game (Hail Mary: How 1994’s pass-friendly rule changes saved a moribund league and created the modern NFL).
All of this simply highlights why, in my opinion, it's hard, if not impossible, to compare players across eras. Derek Carr's been good. I'm a fan. But he's not as great as Kenny Stabler (at least not yet).