Everything all went wrong when companies decided to go to 9/10/11 speeds. Thinned cogs, chains, and sometimes chainrings, makes interchangeability with 8 and older problematic. No more simple compatible swaps with other bikes and equipment in your inventory.
IMHO, for the average recreation cyclist, going to 9+ is simply flushing money down the drain.
But we live in a consumerism society where having the latest and greatest boosts one's self-esteem.