Why all games do not write in Unity?

What's the point of developing their own engines? Is it only in prestige? Why all companies igrodelov not using Unity or Unreal Engine? Don't think for hide the splash screen from Unity for free accounts. Those who have enough money to write their engines enough to purchase a full license. So what is the reason?
July 9th 19 at 11:26
2 answers
July 9th 19 at 11:28
Solution
Why bother to make your own, if you already have something ready? Variants I see three:

1. NIH-syndrome. Developer purely on the principle of trying to only use what he has created, minimally involving third-party development tools. The logic here search is usually pointless.

2. A solution appeared before the other is ready. In the world there are many game engines, created before Unity. Own design has long been used, it is debugged and time-tested, under her curve had a lot of things; throw it in the trash for some newfangled Unity frankly pathetic.

3. A ready solution does not meet all requirements. For example, for a specific toy, Unity too heavy, or does not support some very needed features, or supports, but not well (eats too many resources). "Your" engine for a specific game can be sharpened better that machine will give a competitive advantage over other games made with Unity.
July 9th 19 at 11:30
many do not have enough opportunities Unit or the Unreal Engine, even a greater number lacking proizvoditelny ...

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