I think the title is pretty self-explanatory. It’s another recurring question, so I’m not the only one wondering why the heck refresh/interval doesn’t work on an iframe:
https://community.home-assistant.io/search?q=iframe%20refresh
Edited to add: Given that an iframe could be used for so many different things, I could see the default being no refresh - it’s just puzzling that it isn’t supported at all.