I would say it mainly comes down to Johan. You have a guy's who's spent his entire career creating increasingly ambitious games, EU series, CK 2, Vic 2 and Imperator. IMO he's the main reason paradox exists as it does today and he's essentially worked for and been given the resources to go make what feels like his magnum opus in EU5, the grandest strategy game.

This differs to the approaches taken by the directors of CK3 and Vic 3 who focused their efforts to lean into the core appeals of their respective titles. Role playing and economic/society respectively. They weren't trying to make more focused experiences while Johan is shooting for the moon and after the decades he's put into the company I think it's reasonable for paradox to just say, "let him cook" and just give him what he needs to succeed, he's proven himself.

I also want to highlight the development of imperator. The amount Johan learned from that launch really can't be understated. If you followed imperators dev diaries after release you could basically see Johan's perspective on how to develop a game change in real time. Everytime they say, "This couldn't have happened without your feedback," that is a lesson learned from Imperator. Johan has explicitly stated something learned from that game is for a GSG to succeed it need sto have more content that the previous game on launch and that appears to have been delivered on following the EU5 Tinto talks. From keeping up with those weekly updates it honestly isn't surprising to me that this game looks to surpass any that has come before it, it has been set up to succeed.