"An exemption was made for 'Computer programs and video games distributed in formats that have become obsolete and which require the original media or hardware as a condition of access.'"
EDIT: Actually archive.org posted an article about exactly this [1]
[0]: https://en.m.wikipedia.org/wiki/Digital_Millennium_Copyright...
Plus, they only get you out of the "anticircumvention" provisions, not regular old copyright law or the more familiar DMCA notice-and-takedown procedure. In other words an exemption may allow you to legally remove or break DRM or other copy protection, but it doesn't give you any rights to make copies or display works.
As best I can tell, they seem to be operating on a "see what we can get away with" model, which appears to be working out pretty well for them.
Maybe in the distant future there will be a Geocities Museum that has all Geocities pages because enough generations have passed that putting Geocities sites online by default isn't a privacy concern.
Copyrighted music and video however (stuff that MPAA is interested in) is not available online, and you actually have to go to the physical Archive in SF to access them. In that sense it works kind of like a library.
It's a really awesome place to visit if you ever get the chance!