Because it's a freaking horror movie, that's why, and the Academy gives awards to horror movies like I pay my bills: begrudgingly, tentatively, and with much internal anguish. As to the question of whether Silence is or is not a true "horror movie," I won't even get into it. I could count on three hands the films that have legitimately scared me over the years, and this is one of them. Yes, it's a thriller and a rock-solid cop story, but it's also a great freakin' horror movie ... that won FIVE Oscars.
Oh, and I guess I'm supposed to pick only one scene for this post? Dang, that'll be tough, manly because there are so many doozies, but also because the best ones are just too damn icky. (And I can't be the only one who thinks Ted Levine should have snagged a Best Supporting nod. Dang is he creepy.) Plus most of the best Lecter bits have been done to D E A T H in pop culture, so I'll wish you a good Oscar night and leave you with this clip: