Why are some movies so hard to find?

I have always loved movies. I remember in the 70s watching all the old Hammer Horror Movies on TV. I fell in love with Horror Of Dracula, Blacula, Count Yorga, Night Of The Living Dead 1968 etc...

Being a HUGE movie fan I recall a few years ago that I kept asking myself "Why are some movies so hard to find"? I began researching and building a large collection of rare and out print movies on DVD.

I sold my rare movies on other sites for a couple years and recently decided to take the plunge and open my own online movie store with my own domain tomsraremovies. I am always on the lookout for hard to find dvds that that people are interested in.

I am curious what movies other people looking for and cannot find?