Part of it is that fine dining is much more labor intensive now than it used to be. Chocolate lava cake was at the pinnacle of fine dining desserts in 1987, but now it's considered rather pedestrian.
I don't think that really has anything to do with it being labour intensive, nor suggests that it must be even more so in the post-lava-cake era though. It just 'went viral', was over done (no pun intended), and lost its mystique.
The same no doubt happened to all manner of exotic (or once exotic) dishes before it.
Also a soufflé has a high % of whipped egg whites versus a typical cake which has unwhipped eggs but a bit of baking powder.