In recent years I've lived in two areas in the western U.S. Here's what's happening:
Location 1 is where we watched 20-some publishers grow to 50, build a hall, grow to 180, build a new hall, grow to 240, split into two congos of 120 each. Several years later, one of the halls had 160 attending on Sunday, while the other had dropped a bit to about 100. That's 260 dubs in the building on the biggest meeting day of the week.
That was well over 10 years ago; the last person we talked to from the old congo (last year sometime) said the two congos were still about the same size, but many of the faces had changed. So, in a decade, little or no growth (and no new halls have been built there). Meanwhile, the population of the city there has doubled and is one of the fastest growing areas in the nation.
At Location 2, we moved into a hall that had just split from two to three congos. Ours was the smallest, with about 90 pubs. The other two were over 100. Over the next five years, we watched ours shrink to about 55-60 pubs on Sunday. The other two congos shrunk slightly, to about 90. A nearby Spanish congo meanwhile split twice and finally sent one of their congos over to use our hall which meant four congos met in one building.
The three English congos decided to build a new hall, with prompting from the CO, to handle all the "growth" we were experiencing. So a double-hall (two KHs, one parking lot) was built. A second Spanish congo moved into the old hall. The three English congos now occupy the two new buildings, but their attendance is unchanged.
I should mention that city also has undergone huge increases in population in the past two decades, at least doubling the number of residents!
So, in my experience, there are a lot of "lost dubs" wandering around out there someplace. They are certainly not keeping pace with the population growth, and probably owe that growth for keeping them afloat.