why don't you create your own computer/CPU/drivers etc but isn't that exactly what i.e. Nintendo,Sega, Sony etc did?

Yes, but they and any other examples you are likely to find either a) had no choice, because there was no suitable existing system at the time, b) had experienced developers to tackle to task, or c) both of the aforementioned. If you're experienced enough to create an engine, you're reasonably unlikely to ask the kind of basic questions that often attract advice trying to discourage it, and will no well enough to simply ignore any advice to that effect that you do receive.

I think that there is a lot of benefit to having your own game engine. If you are able to develop your own engine and understand it then it should make it much easier to create the game it'self. The only issue is the time and knowledge required.

Could you not simply spend that time (remembering that given you listed time and knowledge you can include learning time as well as development time) learning an existing proven and well-tested system in-depth? Your argument is a pretty common symptom of NIH syndrome, and whilst there can (as has been covered in some of the prior posts in this topic) sometimes be value in creating your own engine, doing so for increased familiarity with the final product is a fairly weak argument. It should be considered an essential skill for almost any experienced programmer to be able to efficiently familiarise themselves with the usage and capabilities of existing systems.