My view on this........
There is only one reason when all factors are considered.
Poor workmanship: (A poor workman always blames his tools).
Whether it is using wrong or poor equipment and or cleaning agents, too much water, too little drying, being untrained, being inexperienced, misjudging or not checking fitting and or carpet type etc, etc
it all adds up to bad workmanship,
Once you touch the carpet you are responsible for your actions, no outside factors are to blame.
Pre qualifying with the customer potential risks is good practice and good professional CCs should have no worries about shrinkage occurring.
However,
most honest CCs will also admit to at least one mishap in their time.