Primer-BLAST can only find non-specific primers for your template since there are other targets that are similar or identical to your template. You may choose to re-search for specific primers by allowing some of the highly similar off-targets if they are irrelevant to your PCR experiment. For example, not all transcript variants are expressed in all tissues, or you are not concerned about the predicted transcripts (i.e., XM_ accessions), or there are redundant database entries. Another example is, when you enter a raw sequence as PCR template rather than an accession, Primer-BLAST will likely report many off-targets. However, some of these might be your intended target that you should choose to allow. When Primer-BLAST does not need to avoid the highly similar off-targets in selecting unique primer regions, it typically has a much higher chance to find specific primers for your intended target.