I think some of the owners of that era are the reason for the lack of growth, and the NHL had several anti-union owners, from Norris, Wirtz, Ballard etc. They also stifled growth, wanting bigger shares of the pot.
Campbell managed to expand the league to 18 teams in his time in office. Compared to 28 in the NFL, 24 in the MLB and 18 in the NBA at that time. In a league where revenue sharing wasn't even an idea, and the NHL was treading into some very unknown markets already, probably beyond its growth potential.
He's also the first to get the game broadcast in the U.S., and helped its growth, though it was funny to read that NHL owners cancelled their original contract with CBS because they didn't want the NHLPA getting a share of the TV revenues. Those old codgers were the worst I tell you.
Campbell is a legend who started in hockey, grew with the NHL postwar, became a villain in the Maurice Richard suspension, but always understood the game.
Bettman is a businessman who started in basketball, used his marketing expertise to grow the game, and probably thinks he is the best commissioner of all time, for the growth he has created in the U.S, hence staying on to eclipse the aura of Campbell. God help us if the NHL ever names a trophy after him, because he's not really good for hockey, as much as he is good for business.