You don't seem to be accounting for how widely covered Dylan material has historically been. There are plenty of Dylan songs that as far back as the 1960s brought more sales for others than for him. This has continued throughout his career. For example, one 1997 Dylan song was in the top 50 UK sales in 2010 and all told has been covered by more than 450 other artists. In the last five years, official releases of past Grateful Dead concerts have contained at least 30 Dylan songs. It's 600 Dylan songs and at least 10 times that in cover versions which continue earning money.