Not playing PITA here or defending wolves but wolves evolved from time immemorial hunting buffalo, deer and elk, taking the youngest, oldest, weakest and those cut off from the herds. They are opportunists. Never have they encountered defenseless slow animals such as sheep and cattle with no instinct to stampede. Standing in one place to be surrounded meant death on the Great Plains.
A herd of sheep to wolves is like an 'all you can grab free' day at Costco to starving people and the instinct to take down easy prey has no governor.