why ogre3d Irrlicht are not graphically good as unreal engine 3 or CryEngine
Resources. (Time, money, expertise.)
You may have some exceptionally talented people working on the Open Source engines, but the commercial companies will always have people just as good who are being paid full time to make their engine the best on the market.
Let's take OGRE and Unreal as examples.
OGRE is open source. The entire code base is done by people volunteering. They will spend their free time doing it for enjoyment, or just to help. These aren't necessarily the best people.
Unreal is commercial. It is done by paid workers. They do it as a job, and get paid for producing a high quality product. They are very likely to be much better than the average people on open source products.
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