She's releasing material that she wants to, not material that people (the majority of people, that is, not her fans) see as appropriate for someone her age. Cher - Believe is a good counterexample - in that video, Cher was v. much a maternal, 'cool mom' figure. Madonna's still going for 'independent woman' which is cool and I think she can do whatever she wants, but the public aren't on board with women over a certain age doing that.
Let's be honest, how many women over 50 being independent and non-maternal do we see on TV anyway? presenting or talking or anything, let alone being performers or singers releasing pop music. It's an uphill struggle for her.
But having said that, who says she's chasing chart positions? She doesn't seem particularly desperate for them. I personally think she's just releasing singles to make music videos, just because she's Madonna and she can.
Yeah, Ghosttown's not a bad song, but its not the kind of style that's particularly popular now. Once again, people only remember the 'good' songs from yesteryear, the majority of music in the charts is always flavour of the moment. The charts are literally the songs that are most popular at the minute. Sure, you can say they're not great musically or whatever, but that's kind of irrelevant because they don't pretend to be a list of the 'best' songs around at the minute.