Aliexpress short lived sessions. Why?

Hi HNers, I have observed over the course of several months a phenomenon that leaves me baffled. aliexpress.com, the retail website for alibaba, has extremely short lived authentication on its website. They keep users logged in for a few hours at most before having to reauthenticate with username/password.

The alibaba group is no amateur, so I'm inclined to belive this is a deliberate practice, however I cannot figure out what is the advantage of doing this vs for example amazon.com, which keeps users authenticated basically forever.