The reasons primarily had to do with reaching the largest audience, because they were all at heart storytelling attention whores. But really, that's what filmmakers with passion are at their core: they want to tell stories, and they want to entertain other people with them.
Seeing movies in theaters has been around for seventy years or more. Television has been around for fifty, but watching movies on television was really a child of the '70s, and movie-quality storytelling on television is a relatively recent invention.
With the advent of high-def, home theaters, and broadband internet, the world is heading toward streaming content as the new movie medium. As the quality of online media is now to the point of being able to watch almost seamlessly, it's becoming the new medium of choice for this generation of filmmakers.
I've been looking at different avenues for streaming online content. YouTube is the old standby, but the quality has been historically abysmal. They have recently added high-def (720p) capability, but the sheer amount of crap on YouTube makes it a difficult place for a serious filmmaker to get seen.
Don't get me wrong, I've added to the crap on YouTube myself, though I'd like to think I'm a step above the ADVENTURES OF CAT SCRATCH, UNDERWEAR NINJA & BLUBBER BOY 3. (Because there were so many questions left unanswered in the first two.)
I stumbled across Vimeo a few months ago. The image quality is an order of magnitude better than YouTube (IMHO), and they seem to have a lot better selectivity.
For example, I present this short film produced by a young woman in Merry Old England:
Wrath - Short Film from Sam Hendi on Vimeo.
It's categorized as horror, but I'd disagree.
Incidentally, if you watch it directly from the Vimeo site, you can see it in HD. I'd recommend it.
This is someone with similar equipment to me, though a few things that I don't have (like a camera crane and a 35mm adapter) which are things I'm planning on.
It's making me rethink a lot about what I want to do as a filmmaker.