When editing a dashboard card in the Dashboard Card Configuration tool, the preview pane is too small and cannot be resized. This makes it difficult to see the full card, especially on larger desktop monitors where there is extra screen space available.
Usually a card’s width is not big (unless it is a sidebar/panel view or a widened section). So, why would you need a bigger space?
A yaml code could need more space - that is why it is possible to enlarge Editor by tapping on a header.
It sounds like you want this to be a Feature Request.
Those are done in GitHub for all FrontEnd things HERE