The issue is that filming in meatspace is still often less complicated than trying to make those graphics on a computer (assuming your low budget movie has little to no CG). And if you want voices, you still need labor.
If you want to make a movie, it's never been easier! Grab your smartphone, write a script, grab some friends and have them read it, then post.
But from experience, actually making something passible (much less "good" or "great") takes years of dedicated practice, which is more accessible thanks to the above, but still doesn't really make the years any shorter.
The oft-quoted figure is that the production cost of the original Paranormal Activity was $15,000, and that was made before the advent of smartphones.