The trading system is pretty clunky. If you want fair trades that help both teams, without overpaying, you basically have to give them only assets that they want in exchange of assets they're ready to get rid of.
I once traded a young prospect, a 1st and a 2nd to Florida for Aaron Ekblad and they rejected my offer because they didn't want my prospect. I took him out of the deal and they accepted.
In other words, it's as if Toronto refused to traded Matthews to Montreal for Sergachev, a 1st and a 2nd, but accepted for the picks only. This game is garbagio.