`Center` is a result of Flutter having a coherent philosophy (design).
Specifically, instead of doing random mish-mash of layout (like in every other UI toolkit I know, including HTML), Flutter has a simple layout protocol that defines how a parent lays out it's children.
It's a simple, local protocol. ("local" means that the effect of layout is local to widget doing the layout, unlike in HTML where some layout properties effect more than just immediate children).
`Center` is a simple widget that lays out its child in the center of itself.
Why is it good and coherent design?
What if you need to position child 2/3rds on the X axis of the parent?
In Flutter you write (trivial) `Position23rdX` widget and you're done. An easy way to implement custom layout logic that plugs into a coherently designed layout protocol.
In HTML you can't. You can use layout properties that HTML gives or you're out of luck.
I've also worked (or dabbled) with win32 (no layout at all), WinForms, WPF, Cocoa, Gtk - none of them have anything like that.