The problem with things stretching into the season is that the longer it drags out, the higher the first season cap hit becomes on the same overall deal. They use a different calculation for RFA contracts signed midseason:
https://www.capfriendly.com/faq#rfa-caphit
That's why Nylander's cap hit last season was over $10 million and is under $7 million the rest of the way. If he had signed the same 6 year, $45 million deal before the season began, it would have had a $7.5 million cap hit every year.
Last year, that worked out well for the Leafs because they had cap space to spare and it gives them an extra half million in cap space for the remaining years of the deal.
That would not be good for anyone with regards to Tkachuk because the first season of the contract is where the Flames have the cap crunch. They'll have a lot more flexibility in future years.
Allowing it to stretch into the season will ultimately just cost him money.