When it comes to Naruto I am guilty as charged.
But if you compare the Japanese comic rankings now with those of 2008 they don't really have more action series or more variety. They look about the same as far as I can tell.
I don't see any reason to think there has been a market shift. Just a dry spell for series with that kind of potential. I mean, great series do not come along every day or even every year and when they do sometimes Jump isn't the one that gets them. This isn't anybody's fault or something that Jump is in any way responsible for. It's just the way the cookie crumbles.
Would Jump have liked to get more recent action series like Nanatsu no Taizai or UQ Holder? Probably, but they didn't. Thems the breaks.