That's why it's called SAKUGAbooru, not Ongakubooru.

But fr, the more logical reason is that moebooru sites are not able to handle videos with a lot of space on them, with the limit being way less than 100mb. This is especially apparent when sources that are high in quality have sound to boot, taking up more space, so to counteract it, along with other legal reasons (especially since companies are more defensive of even BGM), sound is removed.