a big part of it is because you can use items like orange petals, trapped boxes, and enchanted apples to avoid poison, get out of para, and remove curses. its still considered a must for pvp, and helpful in many other areas, but lots of people find the points better used elsewhere on a lot of pvm builds. personally, i like to run it if what i'm doing allows for it.
I recently swapped anatomy for resist on my Sampire and I’ll never switch back. Having resist for champ spawns is essential for me. The primary reason I would die is when I was para’d or mana vamp and wasn’t able to attack.