Earlier quoted context omitted.
Who are "They" and what does the share price have to do with a new Chairman being appointed?
The rest of the board, and supposedly Musk is being replaced to get a little bit more financial responsibility in Tesla. If Ms. Denholm has a bad track record, then that might not be good news, but I would assume Ms. Denholm was not an impulsive choice, and the board has good reason to seperate her abilities from Telstra's bad performance.
He’s being replaced as consideration for a settlement agreement with the SEC.
It seems likely Tesla chose Denholm because they have a bad PR problem, and it will be difficult for media companies to portray her as a villain.