I dont know exactly what is gonig on in their mind but I can think of two reasons why.
1.) QB's are one of the hardest positions to draft, as far as how they will perform in the NFL. There are alot of busts and subpar players. For example, there are not very many College QB's who wouldnt have had a successfuly career at Miami because they are full of weapons.
2.) There are GOOD quaterbacks in the NFL who just dont have anyone on their team. No matter which QB you take in the NFL today, if you put them on the Bengals, they are not going to the playoffs, I dont care if its Favre or Gannon. What these type of teams need is solid recievers, o-lines, d's, and running backs. Here is a prime example; The RAMS. Did you notice that every QB that stepped in last year did well except the MVP? Take all 3 of those QB's and put them on the Bengals and they will be the laughing stock of the NFL.