From a Moravian website in the UK:
The industrial revolution and 1870 Education Act brought changes to the settlement' way of life and the sisters' house and schools were closed in the latter half of the 19th century. The additional buildings were then converted into dwelling houses which are managed by the Unitas Estates Company. http://www.moravian.org.uk/index.php/uk-congregations-list-for-the-moravian-church/yorkshire-district/gomersal
Its only referring to the closing of a church school connected with one congregation, but it is most likely also involved in the general downturn. After all, the inability to keep religious schools running, and their replacement by a secular school system, can very easily make a big dent in a minority denomination's numbers.
Looking up the Elementary Education Act 1870 we find on Wikipedia:
There were ongoing political clashes between the vested interests of Church, private schools and the National Education League followers. In some districts the creation of boards was delayed by local vote. In others, church leaders managed to be voted onto boards and restrict the building of board schools, or divert the school rate funds into church schools.
The vested church interests referred to there are of the Anglican church, not the Moravians. Losing their own schools and having to send their children to secular or Anglican schools, either one, would undoubtedly have been of great consequence to the denomination's future.
Although divided by an ocean, this article about Bethlehem Pennsylvania seems to tell the same basic story:
Since 1741, Bethlehem has beckoned travelers to experience the warmth and hospitality of this delightful community. In that year, a small group of Moravians settled on the banks of the Lehigh River near the Monocacy Creek.....
On Christmas Eve of that first year, 1741, the Moravians' patron, Count Nicholas Ludwig von Zinzendorf of Saxony, Germany, visited the new settlement. In their two-room log home that housed both man and beast, the Count christened the community "Bethlehem"....
With the advent of the Industrial Revolution, Bethlehem became a center of heavy industry and trade....making the city a "melting pot" of cultures, blending one into the other. http://www.bethlehem-pa.gov/about/history/
And again with LITITZ, PA:
Lititz was established in 1756 by the Moravian Church as an exclusive religious community until 1855, when the town welcomed people of all religious creeds. The town played an active role in the Revolutionary War, Civil War, and industrial revolution, and served as an early musical, educational, and commercial hub. http://www.moravianmanor.org/lititz.htm
Or again :
The cottage industries of the Moravian Settlement were eventually overtaken by the Industrial Revolution and members sought work and business outside the settlement. http://www.derbytelegraph.co.uk/Hidden-past-village-founded-pioneering/story-16865225-detail/story.html#ixzz37ELK0udO
Who has time for 24/7 prayer when you've got to commute?