Fewer Pages Indexed in Google

Has anyone else noticed that fewer pages seem to be indexed in Google if your website hasn't been updated in a while. I have quite a few websites and a couple of them I haven't really spent a lot of time on lately and the number of pages indexed per GWT has decreased pretty dramatically. Other websites which are updated regularly are still fine with the majority of pages submitted via a sitemap showing as indexed but I have never seen such a decrease on a few of my websites.

Just curious if others have noticed this.....

Yes, I’ve noticed the same problem and my traffic is also down this month.