Q:
Why are Karma boosters not in Reward Boost
If it is a bug, Anet has ignored it for years. I don’t recall seeing any specific reason for leaving out the karma boost.
I believe karma boosts are still available as a level up reward.
I don’t believe it was a bug, but one of the ways to alleviate the over-abundance of Karma back then.
It was well-discussed that Karma Boosts weren’t available at the time of the change. There are quite a few new ways to boost Karma implemented since that time. (Food, Guild Boosts, etc.)
Here’s a list of Karma modifiers: https://wiki.guildwars2.com/wiki/Karma#Karma_modifiers
Good luck.
Btw, the bonfire gives you the exact same bonus (i.e booster and bonfire cannot stack).