Only windows in active folder show in workspace.
To compare windows in active folder with some windows in other folder:
Go to Project Explorer.
Right-click the non-active folder and choose Add Shortcuts…
It will open a dialog to pick the window types there to bring to the active folder as shortcuts.
Notice such windows in the other folder show as shortcuts (see Home button on title bar)
Afterwards, these shortcut windows can be deleted. Or right-click the folder in Project Explorer and choose Remove Shortcuts.