ADC was doomed from the start because it powered the monitor. That means laptop users have to buy bulky extrenally-powered converter boxes and it also means yet-more auxiliary power connectors and amperage flowing over the PCI bus for GPUs. LCDs became larger and larger quite quickly, which of course needs still more power.

It may have survived if it was a simpler sound/USB/video connection only. Personally I'm glad to see it gone; I'd rather have to plug 2/3 cables into a monitor than have an Apple-only standard.