It's a combination of a lot of things for sure.
You're right that her synergy with Hurricane hasn't changed itself since the start of the season. But she already does AOE with her rockets, and now she can get even more AOE on top of her AOE with a hurricane in there. From the start, her potential AOE damage potential with hurricane was incredibly huge (also factor in that the bolts can now crit, which is also a big part of why hurricane is so powerful atm).
But Jinx wasn't quite ready to abuse that synergy right away. Right after the rework, her autos felt really clunky. They tried to fix this up a bit in 6.1, but it still felt off. Fast forward to 6.10, about halfway through the season, they further adjusted the attack speed on Fishbones, making her attacks feel a lot better. Then in 6.17, they buffed the ult damage back up significantly, so that it could actually execute things again.
Then you have the shift in the overall game over time, too. Part of it brought on by the mastery changes they made partway through the season. Partially a shift in how mid and top laners tended to play, which allowed the less mobile ADCs to rise back up. And I'm sure it's also partially to do with the tower changes, too. She is a very strong tower pusher, and getting that first tower gold is a decent boost for her/her team.