because they more profitable instead ethereum.
check this link you can fill your rigs configuration her, but this is my profitable coin depend of my rig config https://whattomine.com/merged_coins/3-etc-dcr?utf8=%E2%9C%93&hr_etc=233&fee_etc=2.9&hr_dcr=3750&fee_dcr=0.0&p=280.0&cost=0.1&commit=Calculate