Basically, says Michael Dougherty, because they dominate the Church through its bureacracy. If they left, they would have to build their own bureaucracy from scratch. [I've been looking for this answer for a long time.]
Michael Brendan Dougherty, writing at the promising new site Culture 11, considers why there has not been a schism in the U.S. Catholic Church in his short essay A Schism Deferred
At first the question appears unwarranted. Though one still hears of “AmChurch” in traditionalist Catholic magazines, there is no organized impetus for a split.
Dougherty helps explain why.
Liberal Catholics, he writes, “find their most powerful allies in the hierarchy of the Church... the New York archdiocese alone has over 110 different offices, with some organs of Church bureaucracy dedicated to immigrants, others to diversity, and others still to the promotion of social justice.”
One could add that liberal Catholics of an activist bent also find congenial ground on colleges in the Catholic tradition.
It should not be said that all liberal Catholics are heretical. But those who are must ask themselves: why break away from an institution when we already run it?
“Conservatives, political and theological, tend to be an insurgent force in the Church, establishing new institutions rather than occupying old ones,” Dougherty points out. Just as political conservatives left the media and the academy short of conservatives by establishing their own think tanks and journals (admittedly sometimes because establishment hostility forced them to do so), new conservative or orthodox Catholic groups and journals sometimes leave the established chancery bureaucracies, the charitable foundations, and the Catholic universities to the liberals.
Perhaps they are content with their own fiefdoms of uniformity.
I had taken solace that dissenting groups like Call to Action are aging and powerless. Under Dougherty’s analysis, we see that such groups are merely superfluous. Their needs for networking and information-sharing are served by the faculty lounges or the national conferences for liturgists or catechists. Dissenting ideologies are all the more effective in these organizations when they have become taken for granted. Philokalia Republic
Now, how long will it be before we can clean out the Augean Stables of the U.S. Catholic bureacracy, from bottom to top?