This.
It is so irritating when people say, oh just wait until he hits FA next year, it'll be fine. Some people around here were saying that about pastrnak (example).
Yzerman can't go and tell his agent, hey, we will sign him in FA to a very lucrative deal, just get him to FA and we would love to have him here. That's against the rules. So, if we don't trade for him, then debrincat/agent could argue that we don't really want him at all (now or FA) so let's just get an extension or sign somewhere else before the year is over.
Job security, even if you are a pretty good player like debrincat, is still king. At some point, Max Domi was supposed to be a sure-fire player for multiple teams, but he never did get the extension. Now, look at him. He finished his last contract year and still no extension, has to test FA. I'm sure he'll get paid, but this is very stressful.