I'm sure it's EU thing. If you look on the Seagate HDD's it's even stated on them:
"European Regulatory Address"
I'm not native English, but I think that means it's obligated.
Didn't see it on disks from 2014 or earlier. Since I do see it on disk from 2015 and newer and this "European Regulatory", it seems obvious that it must be a EU legislation most likely.
No idea what's the benefit of stating the address, but the EU sometimes have some odd rules.