The Dark Lord rewards his followers for loyalty and serving well.
Though the Dark Lord may not act ‘nice’ towards his followers, he does promise to reward them for serving him well or remaining loyal to him. Despite his displeasure at Wormtail’s true motivation to return to him, he rewards Wormtail with a new hand for his help recreating a body.
“Wormtail here has paid some of his debt already, have you not, Wormtail?’
He looked down at Wormtail, who continued to sob.
‘You returned to me, not out of loyalty, but out of fear of your old friends. You deserve this pain, Wormtail. You know that, don’t you?’
‘Yes, master,’ moaned Wormtail, ‘please, master … please …’
‘Yet you helped return me to my body,’ said Voldemort coolly, watching Wormtail sob on the ground. ‘Worthless and traitorous as you are, you helped me … and Lord Voldemort rewards his helpers …”
- Harry Potter and the Goblet of Fire, Chapter 33 (The Death Eaters)
He also plans to reward the Lestranges for their refusal to renounce him and unwavering loyalty to him, saying they’ll be highly honored once he gets them out of Azkaban.
“The Lestranges should stand here,’ said Voldemort quietly. ‘But they are entombed in Azkaban. They were faithful. They went to Azkaban rather than renounce me … when Azkaban is broken open, the Lestranges will be honoured beyond their dreams.”
- Harry Potter and the Goblet of Fire, Chapter 33 (The Death Eaters)
Since the Death Eaters typically follow him either because they believe in his plan for the wizarding world, enjoy committing violent acts in his name, or fear him, this seems to be enough. The true believers eagerly anticipate their honor, those who enjoy the violence consider the freedom to do it a reward in itself, and those who serve him out of fear are already motivated by their own fear.