Since the tomato (though not our modern varieties) first evolved in Mexico, isn't there some sense in the idea that it would grow better in hotter countries?
(I'm sure that's not the only factor to which the "our tomatoes are best" advocates would attribute their tomatoes' quality.)
Yeah, tomatoes need a shit ton of sun to really grow well. Although greenhouses help a lot (which is how the Dutch do so well in this market).
Tomatoes also need a bunch of water, of course, which makes them a delicate balancing act in the more southerly (and steadily more drought stricken) regions of Europe
(I'm sure that's not the only factor to which the "our tomatoes are best" advocates would attribute their tomatoes' quality.)