Damn, that's surprising and pretty "based" of him... if there actually was "cause".
On one hand, these sorts of golden parachute things did have a legit use, especially in the time of takeovers, corporate raiding etc.. in the 80s, the exec team ought to act more in line with shareholder interests and a golden parachute helps sweeten things, they know they're going to lose status but they will get their multimillion-dollar pay out if they accept rather than try to block/disrupt some deal which provides value to shareholders etc..
On the other hand these days, these types of deals aren't always popular with the general public, granted Elon is the controversial character here but if this were bank execs getting million dollar pay outs for not really achieveing much and then getting sacked there would be the usual story about the greedy fat cats etc..
What is hilarious is that he's now got access to all the e-mails and the company slack etc. so there is a chance he does have some cause: