Most likely because they can't stop most players from playing in it. Don't know if you've seen this article, but there's a quote from Mets GM Billy Eppler in there:
"In general, we are not given too many opportunities to stand in the way when a player goes (to the WBC). There are certain criteria that has to be met for a player to not go. When we're given that runway, we've taken it. We took it with (Starling) Marte. We filed the objection on Marte because we could. But I don't want to get into the specifics here."
https://www.cbssports.com/mlb/news/edwin-diaz-injury-update-mets-closer-likely-out-for-2023-mlb-season-after-hurting-knee-during-wbc-celebration/
It sounds like, basically, if the player's injury history prevents his contract from being insured to play in the WBC, then the team can prevent it. Otherwise, not.