- Content emphasis
Privacy - If not all your content is public, seeing a different page that represents what somebody else would see is reassuring. It decreases people's anxiety that they might accidentally have made something public that was intended to be private or vice versa.
Simplicity - Although advanced users won't necessarily feel freaked out by seeing lots of options everywhere, new ones might. If your goal is to get as many people uploading content as possible, you don't want it to seem difficult.
Content - The information I want to see quickly on my profile page isn't the same as the information I want to see quickly when I'm uploading a video. But when I go to my profile, you don't have any way of knowing that my goal is to upload a video until I click an upload command. There are many other reasons I might be visiting it.
Speed - Since the commands people want to access when uploading are different from the ones they want to access when doing other things, making a section just for that can make it quicker to perform actions on multiple items.
Consistency - On some sites, users compare their own profile pages to other people's. If you don't have a way for them to see only what other people would see, they can't quickly do that type of comparison... which is essentially taking away a feature.