EA people tend to be in favour of raising taxation. The "giving what we can" pledge is essentially a pledge to voluntarily increase your own taxes in lieu of government taxes.
And they support raising taxes because it's a good way to signal that you're "for the people" and cheap if you care about power more than money. A billionaire CEO will stay a billionaire if their income tax is 90% and unrealized gains tax same as their portfolios growth, and stay a CEO even if they go broke.
The important part for them is power over other peoples lives because that's exactly what you need if you believe you're a special "rational agent" who is responsible for pushing humanity in the right direction. That power can come from shady think tanks, government jobs or controlling a trillion dollar company.