I think it's the opposite! While they may not be the hottest item on the charts or stage anymore, they have a perpetual, legendary popularity that has made them forever part of our pop culture and the soundtrack of the lives of millions of people. Therefore, the bands and songs are well known enough to be immediately recognizable by a large portion of the general public, and that's why companies want to use them in them to sell products.
I think it's a compliment to the longevity and staying power of the bands and their music that this would happen, and a compliment to rock and roll itself that it has finally become acceptable as an art form. Instead of being shunned and criticized by the older people, thanks to an ageing baby boomer population, it's the music that is loved and remembered fondly by them and that's another reason it's being used, to target people who know it and have fond memories of it, and now have money. Twenty years ago, they were still targeting Cadillacs to old people, and rock songs would not have been wanted in commercials.