Early wide angle lenses are interesting because there was a race to see who could make the widest angle lenses, and every millimeter wider was something to shout about in the early 1960s. 35mm was a nice goal because it makes mathematical sense as a step up from 50mm (in terms of angle of view). Rodenstock was another 30mm. Then you have 25, 24, 23, 21mm etc. Each for a short time being the widest available. The Meyer/Pentacon 30mm continued being made for a long time though, I suspect, because it slotted in nicely between lenses in Zeiss's line up (these were DDR companies, there was no reason to produce products that competed head to head).
Strangely, Pentacon did develop a 2.8/29mm lens to replace it. But the 30mm continued on as low priced option, without automatic diaphragm, for years and years. And that's a good thing because the 30mm performs so much better than the faster, wider, 29 that was supposed to take its place.