it is precisely the de-regulation of the religious market and not, as is often assumed, the residue of the “puritan founding” that explains why Americans are so much more religious that Europeans. [Finke and Stark] estimate that rates of religious adherence in the colonies reached their maximum at about 20% and religiosity took off only after previously protected monopolists lost their privileged access to colonial markets (starting in 1776).
From William Roberts Clark in a survey essay on the political economy of religion.
The religious markets approach typically explains variation across time and space in terms of the regulatory environment. In the absence of over-regulation of religious markets, a variety of religious firms hawking variegated religious products can be expected to arise in response to the natural heterogeneity of religious preferences. Consequently, one would expect to find a vibrant religious market where the regulatory environment allows low cost entry of new firms and where state-run monopolies are absent.
The theory also fits with experience in Latin America:
As the Catholic Church lost its ability or willingness to impose monopolies, Latin America countries came under increased pressure from protestant groups who attracted many followers and also spurred Catholics into action
The essay also disputes the phenomena of significant secularisation in Europe:
Stark places one more nail in the secularization hypothesis by arguing that its acceptance has been fueled in part by what he calls the “myth of past piety” in Europe. Current differences in religious behavior between the U.S. and Europe are not the result of secularization in Europe but rather the fact that Europe was never as christianized as commonly believed. In 1551 the Bishop of Gloucester found, for example, that more than half of his 311 parish priests could not recite the Ten Commandments