As do I, because it's faster than browser based email and many GUI clients (like Thunderbird). I also like the fact that I can just copy across my .pinerc file to a new computer and my mail client is setup.
I had not considered the PDF issue. I just open them with an external application. The potential of reading them within Alpine hadn't occurred to me, but now it has, I want it!
It's easy to use, pluggable, and faster than any GUI I've touched.