In the last couple years, I have been seeing many of our macro lenses being discontinued.

Tamron no longer offers any macro lenses, gone is the 180mm macro, 60mm, and recently the 90mm macro which was one of their bestselling macro lenses.

As far as I know, Nikon, Canon, and Sigma no longer offer their macro lenses in the telephoto ranges, like the 150mm, 180mm, and 200mm.

The Sigma and Nikon's 105mm are still available, and Canon still has the 100mm, which in the midrange macro lenses are the most popular. 

Even though many of these lenses are gone, you can still find any of them used with a little searching.

What I see happening, and I've said for years, mirrorless cameras are the future, and I believe you will start seeing many of these lenses coming back, but for the mirrorless cameras.  DSLR sales are losing ground to the mirrorless movement, so makes sense that manufactures put all the efforts into offering more mirrorless lenses.  

I have changed the way I shoot; my Tamron zoom lenses have the ability to shoot in really close to a subject, and then in post processing I just crop out what I want.  With the 26mg camera I can crop a pretty small area and not lose any noticeable quality. No more trying to frame the subject without doing any cropping, which makes shooting so much easier, and less time wasted working to get the perfect framing.