Glad you asked. It’s Because blackface has its origins in white performers blacking up to ‘punch down’ at a marginalised community. Women are no more marginalised than gay men. A drag performer dressing up as a character butch lesbian would be different, as would a white drag performer doing a character of a black woman. In those cases, that would be punching down. That’s the difference.
Drag has its roots in a marginalised subculture of a marginalised community that grew from a rebellion against the idea that the only was to be a man was to subscribe to traditional masculinity. It’s punching up, not down. That’s the difference between ‘woman face’ (give me strength) and Blackface. Drag in its truest form is about men in dresses - deliberately over the top, unbelievable and nonconformist. It’s not about pretending to be a woman and then mocking her, it’s about taking the piss out of the IDEA of femininity and all the things we’re told a woman should be. It’s about ridiculing society’s expectations of both genders by completely over the top characturism and at its heart, drag is self expression. Drag at its heart is ‘this is what you expect of women and it’s ridiculous, and so is what you expect of men’. Drag race and the mainstreaming of drag culture has caused thst to be lost a fair bit and most of the drag community would actually agree it’s not a good thing that drag has become so mainstream. If you think drag is offensive it’s because you don’t understand drag, it’s history and it’s deeply ingrained commentary on society, frankly. If you don’t find it funny that’s a totally different thing.
For what it’s worth, I’m a female drag performer who dresses as a lumberjack and makes penis jokes for pin money, I have PCOS so I grow my own beard if I’m feeling particularly method.