thats cause the value isn't the ONLY signficant thing w.r.t. caps
Sure resistors have value (printed on them), wattage (get use to the size), voltage (50V is pretty standard)
But caps... you got a hell of alot of different voltage rating (some only a volt different), di-electric, ripple-current, temp capability and that is even before you get to the actual capacitance, to which you have a wider range of values, all the way from pF upto F...
There just isn't enough room. Even CaseA Tants have tried to squeeze on the main ones (voltage & capacitance), but have to neglect the others