I agree that the share icons (and the right column) are irritaring (especially how they disappear and reappear when you scroll past full-width images), but I think the text column is kept narrow intentionally.
It has become a rule of thumb that ~680px is the sweet spot for text column widths, since it makes it easier to read. I'm not sure how much actual research that has gone into text column widths, but I know there has been some.