LiPo is an absolute nightmare to ship in nontrivial quantities. The trickiest part is all the paperwork. Shippers really do not like it, because it places a lot of extra restrictions on the way they are allowed to ship it. This is made 10x worse when you are trying to ship bare batteries.

This is also why companies like Sparkfun don't sell batteries internationally. Adafruit used to have this restriction too, but they seem to have recently changed that.