This has only happened to me twice in my career. Once a long time ago, and once quite recently. No matter how many times it’s happened to you, I look at it this way…being an independent contractor or freelance is sort of like dating in a small town.
You never really break up, you just loose your turn.
The reasons why drops happen:
The client changed their minds.
The Dates changed.
The Creative changed.
There was a personality conflict.
A certain creative wants to work with another certain creative.
The client is trying to keep multiple people working.
Someone new in charge wants to bring their old peeps along.
Who knows.
It is what it is, and you may have lost your turn.