Why Feed line loss is attenuation, a ratio of power out to power in, and ratios of power are expressed in decibels, not ohms. Manufacturers publish coax loss as decibels per 100 feet at specified frequencies, because loss rises with frequency. Since dB is a ratio, you can simply scale it: 1.5 dB per 100 feet means 3 dB (half the power) over 200 feet.
Watch out Ohms per 100 feet or per 1,000 feet describes DC resistance of a conductor, not signal attenuation, and coax data sheets standardize on 100 feet rather than 1,000 feet.
Loss is a power ratio, so decibels; cable specs use 100-foot lengths. Think "dB per hundred feet."