It will be very convenient to setup width value of a window where user selects a list item. Or to make it always be as wide as the longest list item name plus width of tabbed white-space due to hierarchy visualization.
This is how it works in Classic UX:

New UX is shrunk too much.

The same problem appears in fields:

Yes, it can be resolved by simple expanding this column or field. But this means less space for another columns at your Page.
Kirill