Question: Why does General Ross keep trying to kill Hulk?
Answer: Because he feels the Hulk is a threat to all life on Earth, and particularly his daughter's close relationship with Bruce Banner puts her at risk when Hulk enters the equation.
Why does Ross think the hulk is a threat?
Because the Hulk is nearly mindless and goes on destructive rampages with high risk of collateral damage.
If that's the case, what's the problem with the way general Ross judges the hulk?
It's nuanced. Ross is correct to recognize the potential danger the Hulk presents, but he's also too stubborn to realise that he usually exacerbates the Hulk's rampages by trying to engage him in combat instead of trying to calm him down.
Question: Why was this show cancelled so quickly?
Answer: I believe it was mentioned in an issue of Wizard Magazine that the show was cancelled because of low ratings, and reportedly the show's creative shift in the second season had a part to play in the low ratings, as the changes alienated fans.
Answer: The Hulk is a giant brute who smashes everything in his path when he is angry. In Ang Lee's "Hulk," General Ross, played by Sam Elliot, explains it to his daughter.