Have you not seen how much the AFCS hates the Colts? It's for essentially the same reasons and it effectively boils down to jealousy.
You guys went from HOF QB to HOF QB while we've all been wallowing in draft busts and retreaded vets for years. Stafford is the best QB to play for the Lions since Bobby Layne was traded in the late-1950s. Cutler is the best QB the Bears have had since McMahon. The Vikings have had better luck with Culpepper(up to the 2005 season) and then only a 5 year gap until Favre.
Even when our teams are good we only have a 1 or 2 season window before the Packers go back to running the division. And when we do have a good team the Packers are rarely bad. With the Colts it's because they just happen to be the least poorly run team in the AFCS. In the NFCN it's because you guys don't have to worry about your team being a family operation. That is a legitimate advantage. When WCF, Sr. couldn't build a winning team and wouldn't ask for help outside of his yes-men and family us Lions fans couldn't do fuck all to truly change things. We had a GM who had 6 winning seasons in 22 years. He retired instead of being fired because he was Ford's guy. Matt Millen was given an extension after fans had been very vocal about wanting him gone. Michael McCaskey royally screwed the Bears in the 1990s because of his incompetence.
Also, it's because of how smug many Packers fans (especially out-of-state) can be. As a Lions fan it is so fucking frustrating hearing shit talking Packers fan every fucking year no matter where I go in the country. You Packers fans just don't really get it. You guys have no problem kicking our fanbases when we're down and then wonder why we're so happy whenever you lose to an NFCN team. Like last year the Lions looked legitimately better than I've seen in a few years and I met numerous Packers fans who acted like Lions fans aren't allowed to be excited about their team. I wouldn't even be talking about the Packers and Packer fans at bars would say things like, "You Lions fans are so cute thinking your team is good." I know the Lions got lucky in a lot of those games and shot themselves in the foot quite a few times (especially in the Wild Card). You Packers fans have just had it so good for so long that there's an entire generation of fans (those born in the mid-80s to present) who don't remember consistently godawful football. The Packers haven't finished last in the division since 1988 when I was born. Meanwhile that same generation of Vikings, Lions, and Bears fans have had a completely different experience and have had to put up with you.
I'm honestly quite jealous of Packers fans being able to see 2 Super Bowl wins in my lifetime. I'm even jealous of the loss. That's why we all rejoice when the Packers lose. We want to know how it feels to root for a team as successful as the Packers. Even when you guys talk about how terrible the 80s were (that many of you didn't experience) you still had five 2nd place finishes and as many playoff wins as the Lions have had since 1958. I don't even truly dislike the Packers I just want their fans to have to experience what it's like to be a Lions fan.