Edit: I'm not talking about "forming a charity". I'm talking about just giving actual money to actual individuals.
https://givingpledge.org/pledger?pledgerId=177
I think he’s already given away more than 50% of his Berkshire holdings.
How many people are there in less comfortable circumstances? 100m? 1bn? Buffett personally doesn't have the time to go handing money to everyone.
He is, probably sensibly, a believer in the conventional system in functional countries - taxes get paid to the government which then has policies to help the less well off.
Because he is advocating systemic changes.
He may very well also give money away to people in need (it seems he does), but this would not actually address the issues he is alluding to here since it would not change the system. Hence there is no value for him to bring it up here.
Leading Democrats seem to hate taxes as much as anybody. ( One of the Biden family’s legal troubles was tax evasion. ). Celebrity mouthpieces from Hollywood are known to take measures to minimize taxes, I.e. Bruce Springsteen calling his mansion a tomato farm. Pols themselves jump through hoops like John Kerry parking his yacht across state lines to minimize taxes.
I don’t see much practical difference in behaviors, really.
On the policy side, while it's true that both parties have been reluctant to raise taxes, I think it's clear that since the Reagan era, it's Republicans who have moved most aggressively to lower taxes, and in ways that disproportionately lower the taxes of the wealthy.