Not sure if your premise is correct, but I'd guess with more wide open offenses, there are more opportunities to get inside the 30 yard line to kick field goals.
I submit the following link...all time NFL field goal percentage. The data is clear cut and ironclad...kickers hit their field goals at a higher percentage now than ever, and are getting better.
1. The 13 of the top 15 are active players. Recently retired Matt Stover was one of the inactive in the top 15. The other is the "Liquored Up Idiot Kicker."
2. You have to go to #41 before you find someone who retired in the last century.
3. You have to go down to #91 to find a player who didn't play after 1989.
4. Hartley sits 8th on the list. Morten is 42nd. Carney is #17. Doug Brien is #35.
5. Of Morten's contemporaries (kickers who kicked in the 1980s), Gary Anderson is first, followed by Nick Lowery, then Morten. Gary is at #36.
6. The Packers really need to replace Mason Crosby.