Hmmm....no SPRINKLER SYSTEM to douse the fire?
Depends how old the building was. Lots of older buildings don’t have fire sprinklers.
When sprinklers are properly designed to match the fuel load they can usually contain a fire. When you have a massive fuel load like ABS or plastic pipe and it is stacked the water from a sprinkler may not reach a fire underneath. It is also easy for a large fuel load fire (like this one apparently) to overwhelm a common sprinkler system.
Plastic pipes are not easily ignited but once they do they melt and create a very intense and noxious fire.