Epithelium tends to act as protective tissues which could be why it is avascular. The dermis specifically has an outer layer that is composed entirely of kertinized dead cells. Cartilage has few nerve endings due to the amount of compression that it withstands. Because of this the compression causes little to no pain and could also explain why it is avascular. Honestly, I was unable to found advantages of the avascularity of these connective tissues in my anatomy notes, test, and books.