Why have your band members changed from time to time?

9 times out of 10.......Because, people lack the dedication they think they have in the beginning, but they do not have the balls to finish, a project, a tour, sometimes even an album or a gig.
It does not mean they are bad people, it just means they are not cut out for the music business.
Imagine you are a great high school football player, and you can score a touch down every time you touch the ball, but it is not convient for you personally to wear a helmet, and you do not like football pads either. Most importantly "you do not want to be part of a team." Yes you could be a football star, you have the tools, the looks, and the skills, but you will not bend outside of your comfort zone and wear equipment, or even care for your team-mates so the team says goodbye to you. Same thing in bands. Guys quit bands everyday because they think they are in love with a girl who breaks up with them shortly after they left the band. Or they want a financial back up plan, or they miss their mommy, or they want their life to stay so small that they control every decision around them.

Everybody says they are in it for the long hall, what they really mean is "dude make me a star immediately with no real effort on my part, beyond what i feel like doing, keep me in my comfort zone, and spell my name right on the check!"