Or maybe Death just didn't care and attacks Soma because despite being his reincarnation he isn't the same Dracula anymore or something?
I figure it's just the guy from the novel who figured "well hey, if Soma is Dracula, wouldn't Death, his best bud and right hand man, approach him like 'yo, Somula, wanna hang out and be a badass lord like you used to be?'" and wrote that in, where IGA and his writers just never considered it.