Well it's not a secret now!!
I think Clinton has made a very good point. The print wears off, which can sometimes look like the area is dirty. The more you clean it, the worse it'll get!
Added to this, the fabric may have been degraded/weakened, especially the bits stretched over the contact points of the arms, so care is needed. Have walked from a few that were starting to split.
Remember if you're stepping in to the world of "problem solvers" on cotton prints to do a wet crock test using whatever solutions you're planning to use for the job. Have seen many a colour rub off on a terry towel testing the ideal product I'd like to use. This, to be honest, is the biggest limiter in results on a lot of cotton prints!