It's because the Golden Knights are a recent expansion team themselves, and so they don't have to give up a player to Kraken, the newest expansion team.
This is based on the agreement the Knights made when joining the league. They wouldn't be part of the expansion draft for a number of years, but also wouldn't get a share of the expansion fee either. See this ESPN article:
The Golden Knights do not have to give up a player in the expansion
draft, a deal owner Bill Foley struck with the NHL in their original
franchise agreement in 2016. The only downside for Vegas? Foley
doesn't get a cut of Seattle's $650 million expansion fee, which
equates to a $21.67 million check for the other 30 teams.
Also as a side note, most NHL expansion teams over time tend to take years, sometimes even a whole decade, before becoming contenders. The Knights are an exception to the trend. Had they followed the usual trajectory, they would've been a mediocre team, with little expectation to be part of the expansion draft.