Why the 'old style' groups are not availible for set-up in the UI, only in yaml

They have an advantage of showing list of elements with their status in the more-info dialog - e.g. showing which window from group.windows is open, or which persons from group.guests are present
The current helper ones just show the history of the whole group

Legacy features that are no longer recommended don’t get enhancements. If there’s something old-style groups do/did well that the new ones do not please make a feature request for that. But enhancements to legacy features (like creation via UI) isn’t going to happen.