And:
1 - have made so much money that you're set for life already
2 - are signing where you have dreamt of playing since you were a kid
3 - are getting an NMC, something which Nylander can't get
Maybe, maybe not. Even if true though, there are other considerations as well (see my 3 points above).
My overall argument is that Nylander is leaving no money on the table, and isn't being asked to leave money on the table, so it is irrelevant as to whether it is easier for one person to leave money on the table versus another, no matter the reasons. However, I'll do my best to respond to each point.
1 - Again, just because Tavares has made money, and will be making more money, does not equate to it being easier to give up money. Most players have accoutants, they pay agent fees, they pay union fees, part of their income is held in escrow, and 'most' players pay quite high income taxes. The more you make, the more expensive your lifestyle is as well. It's not easy or easier for anyone to say "I'll hold on that extra 2M per season".
2 - Again, I don't see this as relevant in terms of contract. It's certainly a reason why he wanted to play for us, however the Leafs were only offering 11M because they had other star players they needed to pay (the same reason the Leafs are reportedly only offering 6-6.5M) and that's ultimatley the biggest reason why Tavares came here. In fact, I think JT got asked at his presser that if the Leafs didn't have Matthews, Marner and Nylander would he have signed here, and I believe he essentially said it may have changed things and it's a big reason why he decided to come here.
3- Exactly. He can't. Every other RFA his age, didn't get one either. Ehlers, Pastrnak, Forsberg, etc all didn't get a NMC. That has no affect on 2nd year negotiations because it's in the CBA that players can't receive one until they are 26 years of age or older. So if he signs a 6-8 year deal, the Leafs can have a NTC in there for years 6, 7, and 8 if he wants. You can't ask for more than similar RFA's because you can't get something they also didn't get either.