What’s with the sweet syrupy stout explosion?

Ok, you can probably tell that I’m not a fan of these pastry, oatmeal, imperial, aged stouts. They are just too cloy, sweet and thick for me. But, I can see that others may enjoy them.

Over the last few years they seem to be increasing at an exponential rate. Is it just interest/demand driven, or is there some new brewing technique or something?

Edit - Let me add that in Belgium, these styles have only been available generally within the last 5 years. Supermarkets are starting to stock them.

I see that perhaps in the US, they’re much lore established.