The fact is we don't know what has gone on beyond closed doors and won't know.
Perhaps Wizz demanded better service than Tui. Never going to happen.
Perhaps Wizz has just decided that they can better deploy the staff.
We only have a Wizz air press release which may or may not be partly true, not true or completely true.
Tui appears to be happy and doing well. While it's difficult to see where the next operator will come in, that's always the case until they arrive.
This market is very fluid and hard to predict
Not that I'll miss Wizz. I thought they were expensive if you needed to take anything with you, and am not a fan of their customer retention process.