I'll admit I don't have a great answer to this, but going from 1920s Paris to 1990s London feels a lot incongruous than going from 1990s Isla Nublar to 2010s Isla Nublar. Perhaps it's because these are all pitched as fully immersive lands in a way that Jurassic Island (or whatever) is not, but it does seem silly that we're being transported through both space and time via the Floo network.
I'll get over it, but it's a bit odd.