Year three is when drafted players are eligible for extensions. If the QB is good, you will want to lock them up to an extension. I suppose you could go the Lamar Jackson route and basically have a standoff. Not sure the Lions want to be known as the team that's too cheap to pay their star QBs.
Goff is under contract for two more years. If you are drafting QB for cap reasons, you better cut or trade him after a year. You can't restructure him since you would be stuck with him for two years so you lose potential cap space in year one because you would have to absorb the full cap hit in 2023 plus the $6-7 million for the rookie QB. They could sign him to an extension now and lower his cap the next two seasons. Given what Carr got and what Daniel Jones may get, probably going to be in the $40 million range. It was just two years ago that Goff's contract was so untradeable that the Rams had to add a 1st round to get rid of him. Now he has a fairly team friendly contract that is pretty tradeable. It will be expense today but in 3-4 years after a couple other QBs sign deals, it won't look as bad. The same thing with Stafford when he signed his extension with Detroit. It was expensive at first and then became team friendly.