Pro-independence has risen in the polls since Brexit. It's enough to give the SNP enough political clout to push for another referendum. Brexit was a remote possibility during the IndyRef campaign. On the contrary, Cameron said multiple times that Scotland would have no guaranteed place in the EU as an independent country, making thinly veiled threats of opposing Scotland joining the EU. Cameron was backed in this by the conservative Spanish government who would very much like to prevent Catalonia from holding its own referendum.