I think one very big reason - and likely the biggest reason - is the Packers have picked their QB of the future well before it was needed. In the case of both Rodgers and Love, they were picked while the established starter was still very effective. Both were able to develop in a backup role for a few years, then Packers management was ruthless in moving on from the previous QB (Favre and Rodgers) to the new QB (Rodgers and Love).
Contrast that to teams that have been bad, picked a QB high, and then they expect that QB to play right away to justify the investment. It becomes a real crap shoot after that. Sometimes, it works (Burrow, Daniels). Sometimes, it doesn't (Young, Williams, Richardson).