Hulkenberg was handed a five-second penalty for causing an opening lap collision with Williams rookie Logan Sargeant last Sunday but Steiner was adamant there had been no contact.
The stewards also ruled that as Hulkenberg was "unable to control the car and was not forced there by any other car" the clash did not get the benefit of the doubt of a first-lap incident.
The German was later handed a further 10-second penalty for failing to serve the first one correctly.
"Nico comes from the inside and is in front basically, dives into the corner, but I can't see a collision," Steiner told reporters at the Spanish Grand Prix.
"F1 is one of the biggest sports in the world and we still have laymen deciding on the fate of people that invest millions in their careers," he added.
"We've been discussing this for years and years and we always go back to this. Every other sport has professional referees... NASCAR, IndyCar, how many times do you hear problems with the stewards or with the race director's decisions? Very rarely."
Every grand prix has a panel of part-time stewards, some nominated by the governing FIA and one by the home national sporting authority, who rule on racing incidents. A former driver is usually among them.
Teams and drivers have complained in the past of inconsistent decisions.
Formula One has used 16 different stewards in six races so far this year, with Singapore's Nish Shetty serving at four of them.
Of the four stewards in Monaco, only 1985 Indianapolis 500 winner Danny Sullivan of the United States had served at a previous race this season.
