Science has a lot less to do with declining religion than being a nation of relative wealth and personal security. Human nature tends to credit their own talent and ingenuity for their success instead of God. Hence, they no longer need Him. Conversely, they will quickly blame God for their troubles and failures. The phenomenon is described quite well in the Bible. As the book of Ecclesiastes states,”there is nothing new under the sun”, and the basics of human nature do not change.
That may indeed represent some of the underlying causes, and may explain why less developed countries are not yet seeing as much of a decline.
But one of the authors of this research paper, Richard Wiener (who is my brother), sees this as more of a networking effect irrespective of specific causes. Just as a language may decline and fade away due to its diminished utility, irrespective of the quality of that language, Richard believes that the same mathematical model can be fitted to the census data for religions in various countries.
Mark 4:19 (New International Version)
19 but the worries of this life, the deceitfulness of wealth and the desires for other things come in and choke the word, making it unfruitful.