请问8老师，为什么I-130批准后要将案子移送到NVC

8老师，关于I-797表上面的表述，我还是有疑问，递交I-130申请时，受益人在美国境内，同时递交了I-20、签证、护照等证明文件，为何不符合境内调整身份？为什么要移送到NVC？移送到NVC是申请签证的必经程序吗？移送到NVC是不是意味着要走境外领事程序，而不能境内调整身份了？麻烦您解答下，谢谢您了！（下面附上I-797的表述）

"The above petition has been approved. The petition indicates that the person for whom you are petitioning is in the United States and will apply for adjustment of status. The evidence indicates that he or she is not eligible to file an adjustment of status applications. This determination is based on the information submitted with the petition and any relating files.  If the person for whom you are petitioning believe that he or she is eligible for adjustment of status, then he or she should contact the local USCIS office for more information.

Because the person for whom you are petitioning is not eligible to adjust, we have sent the approved petition to the Department of State National Visa Center (NVC), 32 Rochester Avenue, Portsmouth, NH 03801-2909. NVC processes all approved immigrant visa which consular post is the appropriate consulate to complete visa processing. NVC will then forward the approved petition to that consulate.

This completes all USCIS action on this petition.  You should allow a minimum of 30 days for Department of State processing before contacting the NVC. If you have not received any correspondence from the NVC within 30 days, you may contact the NVC by e-mail at [e-mail]. You will need to enter the USCIS receipt number from this approval notice in the subject birth, and the Applicant’s name and date of birth, in the body of the e-mail.

The NVC will communicate with the person for whom you are petitioning concerning further immigrant visa processing steps.

The approval of this visa petition does not in itself grant any immigration status and does not guarantee that the alien beneficiary will subsequently be found to be eligible for a visa, for admission to the United States, or for an extension, change, or adjustment of status."