"WHY????" you may scream and shout (or not)
Well, I'll tell ya! It's 3 things.
1. Its focal length. 85mm is considered a telephoto lens. Telephoto lenses (pretty much anything larger than 50mm) are SO flattering for portraits. As wide-angle lenses distort and skew the subject, making the world seem wider - telephoto lenses do the opposite by compressing, or flattening the image, bringing it closer to you. Why is this awesome for portraits? Well, who wouldn't want your nose drawn back in a tad, or our cheekbones raised that tiny bit? What it also does is give you that close, intimate feeling. It's so important to capture that when doing portrait photography. So, I love my 85mm for that reason.
2. It's aperture. It has a wide aperture (or a low f-stop of 1.8) which means it creates a WONDERFUL bokeh (or blurry background). This also gives you that intimate feeling and makes your subject really stand out. It's wide aperture also makes it a great lens for shooting in lower light situations, and who can't benefit from that?! These pictures wouldn't have had the awesome bokeh they have if I had used a different lens.3. It's quality. It's a great quality lens. It runs smoothly, it's focus is sharp, it's just a great piece of glass. LOVE IT! Sometimes, especially if you are serious about getting better than average shots, it's worth it to spend a little money to invest in the good lenses. It will make a huge difference!