Thats a great question! I have to say for me, its because my Amiga does what just about any thing that Windows can do, sure its not super fast. Things made for it though run great. I like the memories of better times. These were times when code was optimised to run on low spec systems, and it did awsome stuff. Its just plain fun too. It works, nevr crashes, and does everything I need it to do.
I also have a high spec PC to do all the oter (mind you a few) things I cant do well on the Amiga.
