Take China National Petroleum Corporation(CNPC) as an example, almost 86% of its stock is stated-owned. Its senior managers' promotion are related to the company's profit. And since there are investors who own 14% percent of its stock, maybe the company will face revenue pressure from them. But I think this is not sufficient to explain why they are so aggressive, I must overlook something more important. Any ideas are going to be appreciated.
You have to distinguish between state owned public service companies and state owned for-profit companies, the for-profit companies are really commercial companies with governments being major shareholders. I would not use the term "state owned" in case of the latter form. Governments can form joint-ventures with private and multinational companies. Governments in this instance would have a special investment management agency or just a fund that are formed to attract investments from abroad. And, in every new joint venture, the government is the main shareholder. So, in CNPC's case, government is a proper shareholder just like institutional shareholders. Since Chinese government is the main shareholder it has the majority of voting rights and would certainly want a good return on investment and they are "aggressive in making profit" as you suggest.
In the former case where the companies, if it can be called a company, are formed to provide public services (think of nationalised train companies), they are not there to make profit, but provide low cost high quality services.