Amazon.com runs on a lot of 20 year old code because they've never been able to upgrade it, because there's so much cruft. Amazon menusand all that create cruft.
There are bugs I fixed in 2006 that came back in 2009 and are still there-- the team that I was on when I fixed them no longer exists because the people got pulled off for nonsense "products" like menus etc that eventually got canned.
It's not just that they are trying things, the things they are trying take engineers out of their key talent pool-- which is pretty shallow to begin with because Amazon is a very anti-engineering company. (Really they hate engineers at the executive level.)
Most of the site at this point is cruft while engineers run around chasing nonsense that will never be in production more than a year.