WWDC is about software. Hardware updates mostly happen later in the year.
Actually, a number of hardware announcements and unveilings have happened at WWDC over the years. A couple of iPhones unveiled, a few Macbook Pros (including last year, I believe, as well as 2012 with the first retina MBP), and a few others.
Maybe WWDC will have less hardware given Apple have so much software now, though.
It's been a while since the Macbook air and pros have been refreshed (no Skylake!), that's why people were thinking it might happen here.