Why would different crossing runways at one airport be on different radio frequencies?
That division is applicable only when the parallels (4's or 22's) are in use, which is the preferential system (see title of chart).

As for rwy 12/30, from the eAIP (PDF; link may die; homepage):

Between 6 AM and 11 PM local:


  RWY 12 and RWY 30 may be used when one or both of the preferential runways cannot be used (...)


Between 11 PM and 6 AM local:


  RWY 12 and RWY 30 are closed for take-off and landing, however, RWY 30 may be used for landings when the crosswind component on the preferential runways exceeds 15 KT or the preferential runways are not available due to disabled aircraft, snow clearance, work on the runways, etc.


Once 12/30 is in use, that chart does not apply. Further:


  During periods with low traffic intensity one or two positions may be responsible for all three area, but apron service will be provided on three separated frequencies simultaneously. The frequencies will be combined by ATC. [emphasis added]