I have no limit and my piles are not necessarily neat.
Do you know WHY you keep switching from one to the next? It sounds like you are getting frustrated.
I have been in a position to where I didn't really want to finish a project but I had no good reason not to finish. Sometimes, it is just a matter of sucking it up and getting it done. Anything else is just excuses.
Sometimes I reward myself with a promise of [fill in the blank] as soon as I finish a project.
What works for me are deadlines. Maybe that would work for you too. Sometimes having a specific purpose in mind helps me keep a WIP alive or resurrect a UFO.
Don't give up and don't beat yourself up. My very first quilt is still not finished. (Started in '89)