Because the agent and player could tell the team that Trouba wouldn't sign with them, which would lower the number of bidders and the price on the player... which... did happen, but through the Jets themselves. Now these things can easily get back-channeled.
There was an executive that said the concerns isn't if teams want Trouba, but rather if Trouba wanted you.
The last two times the Rangers had trades like this, it was for MSL and Rick Nash.... and the Rangers paid full to premium value.
That did not happen this time around, and I for one cannot believe how low the price was. Fair market value would be a young NHL that can step in, a top prospect (1st round equivalent), and a 1st, plus conditional assets if Trouba were to re-sign.
The Rangers got an absolute steal.