They had to take 30 players and not all were going to earn a roster spot - better to let someone walk then to have an unnecessary contract on the books. Vegas took 3 UFAs to be - Thorburn, Brickley and Berube directly walked to free agency a few days after being picked in expansion. Reinhart and Pulkinen never played for Vegas and took up 2 spots in the AHL.
Grubauer was a Vezina finalist and has struggled this season. He was protected in expansion but Colorado failed to extend him and Seattle then signed him as a UFA. Doesn't feel like they did enough of a proper due diligence.