GNOME Files (nautilus) made the file property dialog a modal because they really want it to be centered relative to the file browser window and wayland didn't let them position or obtain coordinates.

The result is that you can't open open two file property dialogs at once (to compare sizes or dates or any other meta data, it's a common thing one might want to do).

Hopefully you'd agree that Wayland should allow apps to position windows relative to their own windows, at the very least.