|Greek priest and his wife.|
The reasoning is the "norm" in the USA is celibacy in the priesthood. I truly don't see this encouragement being any different from St. Paul's "encouragement" in 1 Corinthians 7:7-8 -
7 For I would that all men were even as myself: but every one hath his proper gift from God; one after this manner, and another after that.8 But I say to the unmarried, and to the widows: It is good for them if they so continue, even as I.
Again, this is not a world-wide statement from the Vatican, but directed toward priestly candidates in the United States among Eastern Catholics - because it is the norm in the USA among Catholics. Certainly there have been exceptions to the "rule" - and sometimes methinks the East protesteth too much.