They only need high humidity/a dome when they are fresh, unrooted cuttings. As they continue to transpire (loose water from their pores/stomata), but they have no root system with which to take in adequate water and maintain their turgor, or the water pressure inside their cells which keeps them rigid and the plant erect.
Once they start to form nodules and roots, they don't require high humidity. Typically you can start fresh air exchanges with fresh cuttings after a few days, until the vents are fully open or dome off by 7-10 days.