A trade is tricky. The Leafs would be looking to trade Nylander as a year 1 rental to a team going all in. It's unlikely they will get the return they need to accomplish that same task, as they continue their quest to go on a long playoff run themselves.
To be clear, this isn't the best option for the Leafs. However, with the other options seeming to be harder to obtain as time goes on, letting Nylander walk becomes a better option.
Right now Nylander is on one of the best contracts in the NHL. He is a top-end scoring talent, who performs in the playoffs and is playing for just under 7 million. If the Leafs are looking to go all in this year, they could treat him as their own 1-year rental, especially if they are unable to get more value for Nylander than he is worth this year.