I think some of it is trying to replicate recipes (for those who can’t be bothered cooking …) such as “Nuts & Bolts” which was a great Nibblies/morning tea stand-by, made with Nutrigrain, soup mix, spices, oil & bake. I see that advertised ready-made now.
The marketing people probably trawl instagram & facebook for all the trending recipes to replicate as ‘ready made’ for parents who just don’t have the time or the know-how. Ice cream and (whatever people broke up and incorporated into it) eg cherry ripe, chillies, coconut, rocky road etc.
Cadbury seem to experiment with weird, short lived flavours. I usually get to try them when our ‘warehouse’ supermarket has bought a pallet load of the now discontinued line and has them out for a third of their RR. Milk chocolate and popcorn this week - 170g $1.29. Mr Z liked the first bite, but after two more squares declared it too floury.
I think they get enough people buying out of curiosity that it is worth the short lived new lines.