Short answer: Skeptics doesn't have a Facebook page because Stack Exchange as a rule does not create Facebook (or Google Plus, or YouTube - anything other than Twitter) pages for individual sites.
Both the Ask Different and Photo Facebook pages were created by users. The Ask Different page is (as of very recently) being updated and maintained by Stack Exchange as an experiment of sorts. When the admins of the Ask Different Facebook page found out that they would have a CHAOS member working on evangelizing their site, they offered to give admin access to any SE employee that wanted it. We took them up on that offer. It's not feasible for the company to create a full suite of social media profiles for every site; with over 80 sites in our network, we'd need to double our current number of employees just to manage these social media accounts. And that's not accounting for new sites that get created in the future. However, like I said, the Ask Different page is an experiment to see if it's worth us investing resources in some of the largest sites in our network to develop an "official" social media presence for that site. If it goes well, maybe there will be a threshold past graduation where a site can get more "official" accounts managed by SE if they are big enough.
That being said, we would love to see you, the community, create a Skeptics Stack Exchange site. You'd do a better job of it because you use the site on a daily basis, know exactly what types of content would appeal to other members of your community (both current and potential users of Skeptics), and you can stay on top of hot new content on the site and elsewhere on the web. We at Stack Exchange simply don't have the resources to do that.
Any user is welcome to create a fan community for any Stack Exchange site on their choice of social media platforms. We think it's great! We just ask that you familiarize yourself with our Trademark & Copyright guidelines - essentially, just make it clear in the title and description of your page/account that it is managed by users, not in any official capacity by Stack Exchange.