Titch if Ferrari don't win the driver's title next season then he surely would like to have on his CV that he won drivers titles with 3 teams or more which only Fangio did
Also he would deliver the title after a long wait for them - one over both Vettel and Alonso to improve his status . There is a lot of reasons to do it
Plus Mercedes may not be full factory team in 2021 despite denying this
Also it appears Toto Wolff might be heading towards running the Formula E team which Mercedes want to win having focused their corporate strategy on E cars - they have made a lot of people redundant and refocusing on E cars
It was noted that the person who took the podium celebration at Abu Dhabi with Lewis was actually a Mercedes board member not Toto or James Allison or one of the engineering guys