I think there is a none writed rule with the GM's about not offering crazy money on RFA player
I'd argue that it's not so much an unwritten rule but that offer sheets are difficult to make work based on the NHL's salary cap / compensatory pick structure. There's just a lot of boxes which need to be checked off:
1) Does it even make sense for the player to sign an offer sheet? Last summer, some folks thought Mark Stone was an offer sheet candidate. But when guys are close to free agency, it makes sense for most to keep their options open. So signing a long term offer sheet while giving the original team to match might not make sense. For a guy like Trouba who seems to want to play on the East Coast for family reasons, it wouldn't make sense for him to sign an offer sheet since Winnipeg could happily match.
2) Does a team have the cap space? If so, are they restricted by an internal budget? When the Nylander negotiations dragged on, many folks wondered why there hadn't been an offer sheet. But they seemed to be ignoring how there were maybe 10 teams who had the cap space to make an offer that would be attractive enough for Nylander to sign.
3) Does the team have the required draft picks? So last offseason, the Devils had plenty of cap space but had previously dealt their 2019 3rd round pick. That limited the range of offer sheet that the team could hypothetically offer. Obviously it didn't make a ton of sense to put out an offer sheet at 10.25 million and having to fork over four first round picks.
As it stands, eight teams already moved their 2020 2nds or 3rds. We'll probably see a bit more movement at this draft. Last year there were very few teams who had the cap space, draft picks, and motivation to put out an offer sheet.