why did this couple need a dispensation?

https://familysearch.org/pal:/MM9.3.1/TH-1-18413-54785-48?cc=1874591&wc=3J4Q-GP8:171935001,171974101,176123203

no where in the document did it mention them being related, but yet i found their marriage record here instead of the monte escbed informaciones matrimoniales.