Signing the pledge doesn’t duck you out of any taxes. Also, giv8ng money away can lower taxes you pay, but it doesn’t lower them as much as the amount of money you gave away. Not how it works.
Then they didn’t actually give the money away, and they still aren’t saving or making more money themselves by doing that.
This video explains the scam that Billionaires use:
Why There’s No Such Thing as a Good Billionaire