I was really surprised from the low hits # from mashable, considering the traffic it gets. I think your explanation make sense, but I think I would have got much more hits from TC.
Perhaps, but the problem with both sites is what Jason Kottke calls "infoglut": they are filters with too much content, so readers have to filter the filter. Most readers are going to instantly filter out content that doesn't speak to their audience, and most readers (again, unfortunately) are going to filter out science.
Unfortunately (and unfortunate for many reasons), science isn't a huge draw in a generalized audience (and both Mashable and TC aren't exactly science-oriented).