How come skins unlocked from the Xbox One ver. of Overwatch doesn't transfer to the PC ver. and PS4 ver. and vice versa?

You would think all the content unlocked through the loot boxes be transferable between accounts because it is linked to a Blizzard account. Thus if you want to play with friends on different platforms and want to play with a particular skin you would have to wait a whole year and buy loot boxes for that platform.

Why can't it be accessible on multiple platforms? Is it because of licencing issues or something?