I mean by that logic, Assembly could be deem even simpler, yet writing OR reading programs in Assembly is absolutely not simple at all.

At the end of day, one has to write programs that solve (complicated) problems, and learning how to do that in C is difficult, thus the learning curve deemed higher when it comes to writing professional C.

I can guarantee you that writing professional Go or Java and writing correct programs in both takes way less effort than with C, for use cases that would make Go or Java viable.