Beards are intimidating
As frost giants prefer the glory of combat over the tedium of work, they keep slaves (called thralls) to assist with tasks like preparing food or tanning hides.
The giants make poor masters, often killing these thralls through exhaustion or petty cruelty.
Because they value strength over all, frost giants are sometimes brought under the command of yet greater evils.
In these cases, they are usually glorified mercenaries, who cooperate as long as they're kept supplied with food, weapons, and riches, be it by pay or by pillage.
The giants dedicate their battles to these gods out of respect, and appease them with sacrifices of slaves and treasure out of fear.
The giants are also not above eating thralls in lean times, or when the slaves have outlived their usefulness.
More successful frost giant tribes sometimes capture hardier creatures such as ice trolls or ogres as thralls—these fare somewhat better, serving as shock troops in the giants' war bands.
Frost giants' love of raiding is legendary, and rightly feared among mountain towns the world over.
They have so perfected the art of raiding that they leave enough residents of a town alive that the town can be rebuilt, allowing them to sack it again later once it's amassed enough loot to be worthwhile.