You got the point! You are right, java can start faster and be smaller thanks to binary compilation, such as GraalVM.
I think it’s also possible to do that with Python. I don’t know if it’s stable enough to be used in production, but it’s nice alternative to shrink the image/container size and to speed up (at least the cold start).

However, many developers don’t go deeper and optimize their code in that way. Most of the time because their use case doesn’t required that.
And the computation power required by Fibonacci algorithm is rarely required, especially in serverless architectures.

You can have a look on one of my previous articles on Java frameworks and cold start