The question isn't really, "How is 'The Big Bang Theory' outdated?" —it's where to begin. The very introduction of Kaley Cuoco's Penny sets her up as an object of desire, which gives every single guy in the group — save for Sheldon, who hates her — an opportunity to be an absolute creep to her. (Howard is especially gross when it comes to Penny, whether he's driving around a toy car topped with a camera to see up her skirt or just saying increasingly pervy things to her without worrying about offending her in the slightest.)
As for Sheldon, he eventually learns to love her but still thinks she's an imbecile. Even when the show introduces female characters into the main cast later on — Melissa Rauch's Bernadette Rostenkowski and Mayim Bialik's Amy Farrah Fowler — they're still constantly mistreated by their male partners, whether they're expected to perform every single household chore or simply regarded as inferior.
Then there's the "nerd culture" aspect, wherein Howard, Sheldon, Leonard, and Raj view themselves as dorky outcasts just because they love comic books and superhero movies. "The Big Bang Theory" premiered in 2007. "Iron Man" kicked off the Marvel Cinematic Universe in 2008. For the vast majority of the show's run, the MCU was the most popular thing in the world. Nobody would have made fun of these guys for liking Captain America in the 2010s.
Finally, there's the laugh track. Ever see that YouTube clip of "The Big Bang Theory" without the canned laughter? It's like a horror movie. By 2010, laugh tracks were outdated; this show ran until 2019.
