Why WPF's title bar customization is so uncontrollable and unreasonable

When I write a WPF program, I want to customize the window title bar to make better use of the title bar area. However, it encounters very, very many problems, such as: losing system animations, losing border shadows, maximizing coverage of the taskbar, maximizing beyond the edges of the screen, etc. These problems have troubled me for a long time and have not been fully resolved so far.
In my opinion, this is not a problem that should arise in a modern development framework, and even to say that these problems are very stupid and unreasonable, making me feel that the WPF development process is unpredictable and incomprehensible. In the process of solving these problems at Google, I found many people who encountered the same problems, this is not a new problem, but has existed for several years, whether from the perspective of development requirements or design concepts, these problems should not exist, I need to re-examine the rationality of this framework, I hope this problem can be perfectly solved.