This Wikipedia article Roman Catholicism in the Netherlands shows that the number of Catholics both as a percentage of the total population and in numbers has declined from 1970 to 2013 (40.5%/5.3m to 23.7%/4.0m).
Within the Catholic Church, what are the main reasons given for the decline of Catholicism in the Netherlands? Are the reasons the same for the decline of Christianity in general within the country?
Please note that if an answer mentions "secularization" as I read when researching, the meaning of this is to be borne out in the answer. To me it come across as "I am no longer religious because I became non-religious."
Seeking an answer from first hand Church documents/sources.