Why does the pineapple always ripen/soften from the base?

As per the consensus under this post, lacking ethylene the pineapple softens but not ripens after picking. But it seems even before or right after picking the pineapple is ripe only at the bottom. Does it ripen from the bottom while on the plant because the base is connected to the stem? But why does that lead to the bottom ripening first?

Also my pineapples always ripen/soften from the bottom. It has become a pet peeve of mine that when the bottom is nice and soft and sweet, the upper 80% is still green and hard, but when the upper pineapple reaches the middle part of the softening process the bottom usually seems over-ripe, starting to rot. Why is that? I have seen posts here where people say they store their pineapples upside down. Is that necessary?