Because there is a difference between what a team accomplishes and what a quarterback accomplishes. His quarterback stats consistently put him as ranking between 15th and 17th in the NFL. This year on probably his best year ever, his stats placed him at a ranking of 12th best in the league. That's really low for a guy who had the top paid salary in the NFL for a short while.
Flacco is sort of like Terry Bradshaw. Bradshaw was a good quarterback but not a great quarterback. Have you ever noticed that his name is NEVER mentioned with the all time greats like Montana and Marino and Elway? And heck, Marino never even won a Super Bowl. The reason is because they are looking at the quarterback's individual talent, not the team's talent. Yes, Bradshaw won 4 Super Bowls, but because of his team's great defense.
Flacco has been on a great team with one of the top defenses in the league since day 1. That is why he has such a great record.
The veterans on Flacco's team last year made a huge difference in how that team did, not Flacco. Take last year for example. Those veteran defensive players were all out injured the last 5 regular games of the season. What was Flacco's record during that stretch? It was 1 win and 4 losses. He won only 20% of his games with those defensives veterans out injured. Luckily for Flacco, the Ravens got them all back healthy to start the playoffs.
The other thing is when people watch video of Flacco play. Most of the time he doesn't impress all that well. Yes, he did some in the playoffs. That was probably the best playing of his entire career. But team wins without the stats to support it, especially when a QB is playing for a veteran team doesn't really mean he's all that good. Look at Mark Sanchez for example. People could make the same kind of arguments for him. In fact, many times his stats were nearly as good as Flacco's. He made it to 2 AFC championships in a row. Yet people say he sucks.
What I remember most when I watch Flacco play is that his drives often stall when he is forced to pass the ball. Now some of that is due to Cam Cameron and his offensive play calling. Heck, even I could guess most of his play calls. Cameron was not very inventive on his play calls. Having Caldwell has helped.
Flacco is a good quarterback. And at times he can throw the deep ball well. But he's nowhere near the caliber of elite quarterbacks like Peyton, Brady, Rodgers and Brees. I think even Andrew Luck will soon pass Flacco.
Flacco also tends to struggle on the road. He does very well in Baltimore. But on the road he struggles with the weakest teams in the NFL like the Chiefs last year and got blown out by the Texans on the road. And honestly, the Texans weren't all that strong last year.
I think we'll get a better idea of how good or how bad Flacco is this year. A lot of those veterans are gone this year. Luckily for Flacco, the Ravens had a lot of depth of talent and a great coach. So they may still do pretty well. However, I think that huge salary of Flacco's over the next few years is really going to hurt the Ravens. The Ravens will have to depend more and more on Flacco's ability because of how much his salary and the salary of other veterans will eat up of their cap space. That is eventually what forced the Colts to get rid of Peyton even with as great as he was playing.
Eventually Flacco's highly overpaid salary will cause a meltdown of the Ravens quality. It may not happen this year or even next, but it will eventually happen. The only way the Ravens can stave that off is by keeping a really young team or by eventually getting Flacco to take a huge pay cut like Brady did which I don't think Flacco is nearly as giving as Brady in that regards.