C++ gives you immense power and a huge range of functionality to choose from, and some of the complexity arises from this. It has a very long history, which also contributes to the complexity. And it's first and foremost a pragmatic language, which of course brings in some complexity in order to deal with the inherent complexity of reality.
If something is seen as "complex" in C++, there's usually a good, or at least understandable, reason for this. You can usually find technical documents or discussion that justify why things are they way that they are, and the reasoning is usually quite sound. And in many cases, it's possible to safely ignore or just not use large portions of the complexity that C++ offers without facing any sort of a penalty or harm.
It's very different from the complexity that languages like JavaScript or PHP bring. The complexity there is usually unjustifiable, and often due to very rushed work, a lack of understanding and poor design, or a lack of care and consistency. They suffer from serious flaws and complexity that were not justified when introduced, and were subsequently not cleaned up or fixed once recognized. They suffer from harmful complexity, while C++ offers beneficial complexity.