This isn't to say that mega-churches are a sign of spiritual health, just an observation that conservative Christians express their faith by gathering together in a way that progressive Christians do not. Relatedly, many high profile voices within progressive Christianity do not go to church.
Church it seems, at least in it's traditional expression of gathering on Sunday mornings, is either hard for progressive Christians or is not as valued.
Why is this the case?
I think the some of the answer if found in the work of the psychologist Jonathan Haidt. According to Haidt human societies, large and small, appeal to different "moral grammars" or "moral foundations" in order to make moral and social judgments about what is "right" or "wrong." Haidt's research has identified five general moral foundations: Care, Fairness, Loyalty, Authority and Sanctity.
As observed by Haidt, liberals tend to restrict their moral judgments to the foundations of Care and Fairness. That is to say, liberals tend to judge something as "wrong" if it involves harm (a violation of the Care ethic) or if is unfair/unjust (a violation of the Fairness ethic).
By contrast, conservatives appeal to all five foundations. Beyond issues of harm and injustice conservatives also care about in-group loyalty/solidarity, obeying authority and honoring the holy/sacred.
For our purposes the relevant contrast is how conservatives, by and large, care about group loyalty in a way liberals/progressives do not, or at least not as intensely. Conservatives tend to be pack animals. Progressives tend to be lone wolves. Conservatives value community and group solidarity. Progressives value autonomy and independence.
Also important here is how conservatives have more respect for authority, giving more deference to traditional cultural institutions like the church.
To be clear, this does not mean that progressives don't value relationality. They most certainly do. What progressives struggle with isn't relationality but with loyalty to a group that is larger than their immediate network of friendships, a group that includes people who might be acquaintances and strangers. And lacking this impulse progressives appear to lack the social dynamic that pulls and holds large numbers of people together. Consequently, church for progressives tends to get no larger than one's immediate network of friendships. More often than not, when progressive Christians describe their "church" they describe shared meals and life with their friends. Which is all to the good, we're just describing the dynamic that seems to be at work.
So is this why we don't find many progressive mega-churches?
--from an unpublished post exploring the psychological dynamics that affect progressive and conservative Christians in relation to church-going