It is not about what he thinks he is worth, it is about his market value.
Like selling you home, Ofcourse you want it to sell it as high as possible, but will buyers pay that amount is a completely different story. If people are only offering 20%less than your listing price, it is a pretty good indication that your home value is actually 20%less than you think.
If there are teams that is willing to offer Marner 12mil/8yrs, that’s his value. But if other teams at best are offering 9mil/6yrs, why should the Leafs overpaid that amount? Bc Dubas paid Willie a 7mil contract a few months back- where this contract is also looking pretty much considering all the new contracts being signed? Or bc Matthews is getting 11mil plus, where is Matthews is RFA, teams would probably offer 13mil/8yrs for his service?