Some other useful facts:
The average ECUSA parish gets only 77 a Sunday.
The largest ECUSA parish in America (Christ Church in Plano, TX) gets just under 2100 a Sunday. There are several dozen churches of denominations ranging from Assembly of God to Roman Catholic in my city alone that top 2100 a Sunday. And you guessed it, Christ Church is highly evangelical.
The average active Episcopalian is over 55.
It's a budgetary device: no need to provide extensive/expensive children's ministries, especially true with the denomination's increasing outreach to queers.