Because supposedly there's speculation going around that Trouba wont play in Canada. He only wants to play in the States hence one of the reasons why he wants out of Winnipeg. But as of now it's mere speculation and Hearsay until we know more.
What difference does it make? Trouba doesn't get to decide where he goes. This isn't one of those NTC/NMC situations where a player can veto a trade if he doesn't like the destination. He doesn't get to give Winnipeg a list of places he can't get traded to.
Not only that, but it isn't like the teams trying to acquire him get to negotiate a contract first. So how is he going to stop someone from offering Winnipeg a fair trade? His agent sure doesn't get invited to the trade negotiations, and Cheveldayoff isn't about to do Trouba any favors by only dealing with teams he wants to play on.
If Trouba is trying to dictate his destination at the same time as holding out, then he is less likely to get dealt at all. And if he is traded to a Canadian team, and he complains about that, too, then he is flushing his career.
I don't think the speculation that he doesn't want to, or will not, play for a Canadian team is absolutely bogus!