It makes no sense that customizing the tool bar is limited in that the default tools can't be deleted or even moved lower. Same goes for the side panel. Same goes for the navigation bar. Everyone uses the product differently, requiring/preferring widely varied views and tools. I don't see why adobe wouldn't provide full customization in order to better serve every user. Some of the default icons are ones I will absolutely never click on but I have no choice but to have and keep them in the prime and easiest to access locations on the page.