They don't have to make one. They want to make it.

Idk why people still didn't get that these rules are made to replace Rally2 in long term while co-existing with them in a short term. It's there to allow manufacturers without eligiable base car (which almost all of them have Rally2 car now) and to allow private projects to be homologated, so there will be no more Corsa R5 or Mitsubishi R5 cases.

Still would be better to also allow to build the car on road-car chassis, but there are still Rally2s and there isn't any info of a plans to scrap them.