The ones that look old are old. The USG has newer design systems that you'll see used on many of the websites that have been redesigned more recently: https://designsystem.digital.gov/

This admin gutted both NOAAs budget and workforce so a website redesign is probably low priority at the moment.

Sites like NASA's APOD have not changed by design. So many third parties have been built up around sites that any change [w|c]ould break so much for no effective gain. Same holds true when people ask why things like NOTAMs and even NOAA's alerts are formatted the way they are.