Most of those churches have spawned traditionalist offshoot groups, or traditional mainline denominations which decided to move away from liberalism, which are fast-growing. The decline of the PCUSA is accompanied by the rise of ECO, the PCA and OPC. The decline of the ELCA is accompanied by the rise of the NALC,
Some groups that left the ELCA had other motivations besides disagreement with statements on human sexuality. For instance one offshot group rejected episcopal governance, and left around 2000 because the ELCA sought closer ties with Episcopalians. Even in the recent NALC formation a few years ago, they also rejected episcopal polity, though not in quite as strong terms.
I find this idea of rejecting episcopal polity a bit problematic as a Lutheran POV, as our confessions are actually not against this ancient form of church polity, and several Lutheran churches do in fact have episcopal governance (the ELCA actually has bishops though their "diocese", or synods, are huge). Sometimes, like in the ACNA, there are international powerplays happening, effectively jostling to manipulate a minority perspective into prominence. So my point is that there is other stuff going on other than just human sexuality. Though that issue is the most symbolic.
Even if you consider that many of these groups have genuine objections against this perceived excess in permissiveness, they are still a small fraction of all the mainline in the US. Though they are an option for the dedicated seeker (since they are far fewer in number), someone interested in the general ethos of mainline Protestantism but concerned about the direction that most churches have taken.
However, compared to the large number of American fundamentalist evangelicals that the author of this webpage is writing about as "faithful" to the Scriptures, these churches that recently broke away are otherwise historically liberal. Many having female clergy, critical methods of reading the Scriptures, and so forth. We may be sad there is a breakup, but they are still part of the liberal mainline in many ways (unlike say, the Continuing Anglicans, who have left that decades before these issues came to a head, though I've seen higher critical methods acknowledged in some of those churches as well).
I am aware of converts to Orthodoxy but if you look at the numbers it's a small fraction compared to the people that are leaving Christianity altogether and becoming nones. And my experience is that not all converts to Orthodoxy are retained, and that this is an unspoken problem. I know several on this forum and one in the real world (and no I'm not talking about me) who don't participate in their church or have effectively excommunicated themselves, likely never able to return, and moved on with their lives as spiritual but not religious or nones.
What's my point? Don't ask for whom the bell tolls, it tolls for thee. All the churches in America are going to be facing serious problems within a generation.
