Because it's actually been answered before (just not by me)
If you leave him a year short of UFA, he doesn't have to take anything longer than a year contract wise. He's an RFA with arbitration eligible rights. So he sits tight, goes to arbitration, an award is handed out and he's a UFA the following year with quite possibly a lot of resentment. Thus, signing him a year shy of his UFA is not a cure all. You cannot force him to take years out of his free agency. If you want to get around that, maybe you need to kick out the possibility of signing him to a 5 year deal as well. So now we are looking at 3 / 4 (to potentially sign him to a long term deal at that point , but if he outplays that, that second contract in 3 to 4 years could be considerably greater. Say he settles in at 50-60 point per season over the next three. Well, we are going to have to give him a good amount of money when he's up again.
Secondarily, we don't know what the labor landscape is at that point in time. How do we know that the terms of free agency aren't different? Maybe, when a new cba is signed, one of the things that is altered is when they can hit UFA and he hits it anyway.
Thirdly, I'm not concerned about 6.5 years down the line with him. I'm just not. I can't get people to be concerned about signing Palms to a bloated contract for 5 years down the line that will probably not age well, but now I'm getting blow back for not having enough foresight to want to shut down signing a 21 year old a year shy of unrestricted free agency. This whole thing is ass backwards.