they have all of the music
Actually, they don't. To remake FFVII, or any game, sure, you have source material, but you don't have the exact music to reuse; like, take Pokemon FireRed/LeafGreen. They didn't use the same exact music from back in the day, that would have been ugly, using 8-bit music on a 16-bit remake. What did they do? Arrange it on modern hardware for the system. Flash back to modern day. FFVII had, well, some ugly-sounding music (to me, even by standards back then). Nowadays, we expect games to have an orchestral score, especially games like Final Fantasy. Subtract Nobuo Uematsu from the modern day possibility of an FFVII remake since he is at Mistwalker Studios now. Not only do we not have the inability to use the original music in its exact form, but we do not have the original composer to work with it. SE would need to get the right to arrange Uematsu's work. If they can't, then bam, we get an original soundtrack in the remake of FFVII.
Back on topic, hyperbole much? You can update level designs, yes, but still, it doesn't seem like it'd take more than, what, four years with current generation technology?