Everyone wants to feel wanted in their jobs/careers. The Packers may have extended an offer to Jennings, but I believe Jennings stated the Vikings REALLY made him feel wanted. I can relate to this. I just moved across the country (NC to CA) for a new job because the new company made it VERY obvious they really wanted me. Even if the location isn't ideal to the individual, feeling wanted and as an indispensable entity in the organization is very important. I wouldn't be surprised if Ted Thompson's approach is more reserved in dealing with some players in terms of stroking their ego. I could see him acting like "Well, we'd like to have you back, but here's what we're willing to pay you. If that's not good enough for you, I understand and wish you luck. Talk to you later."
I don't blame Jennings for going to the Vikings, especially since I don't know all the facts and what went on behind closed doors. Teams can turn around quickly, anyway. For all we know, the Vikings could have the next Aaron Rodgers/Andrew Luck/Russell Wilson in a year or two and be a completely different football team, perhaps even a contender. Take the best situation, and see what happens.