In the book, Barty Crouch Jr. tells Dumbledore under the influence of Veritaserum
My father had left the tent; he had gone to free the Muggles. Winky
was afraid to see me so angry. She used her own brand of magic to bind
me to her. She pulled me from the tent, pulled me into the forest,
away from the Death Eaters. I tried to hold her back. I wanted to
return to the campsite. I wanted to show those Death Eaters what
loyalty to the Dark Lord meant, and to punish them for their lack of
it. I used the stolen wand to cast the Dark Mark into the sky.
He was disgusted by the behavior of the "free" death eaters who had not bothered to look for their master when their own powers were intact. He wanted to frighten them & remind them that their sole purpose should be search of dark lord and not idle time pass of muggle torture.
Voldemort himself mentions it during his rebirth
“Lucius, my slippery friend,” he whispered, halting before him. “I am
told that you have not renounced the old ways, though to the world you
present a respectable face. You are still ready to take the lead in a
spot of Muggle-torture, I believe? Yet you never tried to find me,
Lucius...Your exploits at the Quidditch World Cup were fun, I
daresay... but might not your energies have been better directed
toward finding and aiding your master?”
..
“And yet you ran from my Mark, when a faithful Death Eater sent it
into the sky last summer?” said Voldemort lazily, and Mr. Malfoy
stopped talking abruptly. “Yes, I know all about that, Lucius... You
have disappointed me... I expect more faithful service in the future.”