There is a LOT of kruft in the MP, despite that big purge some years ago. I believe that having that field would be useful because a smart merchant is not going to let that date get too old before making update to the page. Absent merchants are not going to update their listings and thus buyers can see the old stuff for what it is. Sure, I will concede that some old stuff is just as good today as it was at the start. Some of my items from 2016 are still top sellers, it happens. More often though, I think older listings harbor a lot of junk that should be avoided.