What problem does this address?

The navigation editor implements its own version of accordion style menus:
https://github.com/WordPress/gutenberg/blob/trunk/packages/edit-navigation/src/components/editor/style.scss#L15-L108

Because these styles aren't part of the block, they're very brittle and can break easily when the block's own css or classnames change.

What is your proposed solution?

Ideally they'd become part of the block itself, maybe as a block style?