Largely because I am forbidden, professionally, to use anything that would attach a GPL licence of any kind to my work. I had a lot of trouble getting permission to use the openSSL libs, which are under Apache licence and available for private and commercial use.
My 2 cents here is that while the FSF were very good for the software industry in the beginning, they have become extremists. Extremists in anything are detrimental and destroy more than they create. I can't/won't support them any more.