I think the point is that some cosmetic TLC would improve matters considerably.
The basic frames have years of life left, but they have the same feel as a house that has been rented out for a few years, rather than lived in by an owner.
The 767 short haul fleet suffers from the same affliction, to a greater/lesser degree, depending which one you get.
I travelled twice on 777 IA from LGW at Xmas, a 15 year old aircraft, so not too far away from the 737s.
She was in tip top cosmetic condition.