I don’t really know any Hertha fans personally as I’m an Union guy (just went to Hertha for the novelty of Olympiastadion/Europa/playing Dortmund) but it wouldn’t surprise me as although it’s an amazing stadium it’s pretty difficult to drum up much of an atmosphere BUT THAT SAID Hertha fans are a bit nothingy so it can’t just be down to the ground.
Tbh the Olympiastadion is such a money spinner for tourism they can’t really afford to play anywhere else (there also isn’t really another suitable stadium for them)