I think Supes is afraid to go all out. For the thread let's just say that they have similar strength, endurance, durability and they are fighting h2h. Supes would realize;
1) This guy gets stronger the more I fight him. I'll lead him away from innocent people. Supes leads Hulk away from people and finds out the Hulk isn't as strong as before. Supes thinks to himself "Hmmm, if I let this guy calm down, maybe he won't give me any trouble. Supes flies in the sky and keeps watch over Hulk. The Hulk calms enough to turn into Banner. Supes goes to Banner and takes him to the JLA headquarters to keep everybody safe. Brains beats strength.
2) Supes if fighting Hulk h2h and sees the destruction occurring and decides to see how super speed works on Hulk. And sure enough, the Hulk can't adapt fast enough to counter super speed. Super speed beats strength.