Why? Well most of us here don't work for Adobe, we can't tell you why. However, it was announced on April 21, 2015 (the day Lightroom 6 was released) that this would be the case, that LR 6 would receive bug fixes and new camera/lens support, but no new features (see: The CC Photography Plan Keeps Getting Better: All New Lightroom CC and More Available Today! | PHOTOSHOP.COM BLOG).
Is there anything you can do? You could subscribe to LR CC and receive those new features (and Photoshop too)
When you pay more you get more, which will be LR 7 for you.
In the mean time you can at least get to the Dehaze slider via a plug-in (not just presets) in LR 6: