Why aren't my supply drops a good rarity?

I started my world 5days ago and got 3 of my friends to join, all of us are level 60-80, anyways I got another friend to join recently and he's lvl 15 when pointing this out I also realised none of the supply drops where a good rarity, with most of them being grey, the highest rarity I have got was blue.

I suspect it might be because someone is a low level the supply drops are but I'm not sure. My supply loot multiplier slider is max.

Can anyone help?