Because it is not Catholic.
However, since the Catholic Church and the Greek Orthodox Church are also Christian and predate the multiple Protestant denominations by over 1,000 years, why do these Protestant denominationalists call themselves the "Christian Adoption Agency" while excluding non-Protestant Christians?
If they serve only Protestant Christians, they should identify themselves as the "Protestant Adoption Agency".
If they serve only those Protestant Christians that share their particular beliefs, they should identify themselves as the "Protestant Except for the Lutherans Who We Think Are Too Much Like Catholics Adoption Agency" or whatever other restrictive name accurately describes them.
well said.