For one thing, pitching/hitting styles changed. Stanley averaged 157 IP a year from 1977 to 1983, mostly in relief. But he also had a K/9 of 3.2 for that period. That's not a typo, and it's not his BB/9, it's his K/9.
That's extreme, but a lot of the high-workload relievers of that era, like Marshall, Tekulve and Quisenberry, also had very low K/9s by modern standards. They were pitching aggressively to contact, exactly the opposite of what we expect from high-leverage relievers today. Unfortunately we don't have pitch count numbers from that era, but I'll bet you that Bob Stanley, in throwing 150 innings, threw not a whole lot more than half as many pitches as it took Chris Sale to do the same thing--because many, many of the PAs were ending on the first, second, or at most third pitch. If you watched Stanley in the early 80s, that was what made him so painful to watch when he had a bad outing--the hitters were all over the first pitch, and you'd be looking at runners at the corners and a couple of runs already in almost before you had time to blink. At the same time, when the sharp grounders and fliners were headed to the right places, he could be dizzyingly efficient by modern standards.
I don't know if you could get away with that style today. Is anybody?