The biggest drawback to an active radar homing missile in the 50's to even into the early 70's is one of how much power you can cram into the missile. Tube technology draws a lot more power than solid state, and radar technology at the time was not able to use detection circuitry that could run on a low-power signal resulting in an often miniscule return. Add in that battery technology was more limited and batteries of that era, in general, didn't have the greatest shelf life. So, needing a lot of power and a big (and likely heavy) battery to provide it was going to be a serious issue.