I think thats a reflection of the position rather then the individuals, i think the margin of error allowed for in the backrow is greater then other positions on the field, i think they can do less wrong then other positions. The expectation of them is to work hard, make tackles and hit rucks. If a back-rowers accuracy at the ruck or tackle is off marginally, you dont really notice it. One ineffective tackle or one poor clean out doesn’t usually change the game. Whereas i think mistakes in other positions magnify the impact on the teaml.
A a fly-half will be crucified for one bad pass in the game, a hooker will be remembered for the lineout throw he got crooked, a kicker will be remembered for the kick he missed and a prop will be remembered for the one scrum he got wrong. Conversely if they get it right they get praised, but I think the metrics which they are judged by are a high bar which are difficult to hit consistently.