Certainly, being below a certain threshold would be one important factor.
He was a contentious figure, and Uber might want to see him off - remember that he got in a huge boardroom war with other board members - so this is likely something they want. His departure could have been part of the long term deal, or possibly in his contract somewhere.
Though there's definitely cred in having the founder around, I suggest this is not that kind of situation.
There's only so many board seats as well, there may have been angling for others to step in.
Personal choice matters a lot as well - he simply may not really want to do it for a variety of reasons.
To me it seems there are no hard rules for boards: it's not like hiring staff or even execs wherein you're generally looking for things, often, the board is just the 'gang of people with the power' duking it out for influence and control etc. so things can be very nuanced, political etc..
Certainly, being below a certain threshold would be one important factor.
He was a contentious figure, and Uber might want to see him off - remember that he got in a huge boardroom war with other board members - so this is likely something they want. His departure could have been part of the long term deal, or possibly in his contract somewhere.
Though there's definitely cred in having the founder around, I suggest this is not that kind of situation.
There's only so many board seats as well, there may have been angling for others to step in.
Personal choice matters a lot as well - he simply may not really want to do it for a variety of reasons.
To me it seems there are no hard rules for boards: it's not like hiring staff or even execs wherein you're generally looking for things, often, the board is just the 'gang of people with the power' duking it out for influence and control etc. so things can be very nuanced, political etc..