I cannot suggest why the infinite impedance detector wasn't more popular except to guess that it may have been for reasons of cost.
However going very slightly off topic if I may. Many, including me, may not be particularly familiar with the II detector, (probably precisely because of its lack of popularity) so here is an excellent explanation of how the II detector works from Al.
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Originally Posted by Skywave;
The conventional valve-based infinite impedance detector is a derivation of the anode-bend detector. However, in the infinite impedance detector, the output is taken from the cathode, unlike the anode bend detector, where the output is taken from the anode. Hence, the infinite impedance detector is a form of a cathode follower (CF). Therefore the input Z is extremely high owing to the 100% -ve feedback and as with a CF, the anode needs to be decoupled: in this case, to RF and AF. The resultant signal at the cathode will contain RF and AF components, so a filter at the cathode is necessary to remove the RF components. It is usual to add more filtering than a simple capacitor across the cathode resistor, as in your example***. Note that there is a critical minimum value for that capacitor. If its capacity is too small, the input to the valve will appear to be a negative resistance when 'seen' by the IFT and the whole stage will probably become unstable. The output Z of a CF is approximately equal to 1/gm, where gm = the mutual conductance of the valve, and in the infinite impedance detector, the value of the cathode resistor should be fairly high compared with 1/gm: something like 20 kΩ to 47 kΩ is not uncommon.
Since the infinite impedance detector is a form of a CF, its voltage gain will be less than unity, but on account of its very high input Z it will present a very minimal damping on the tuned cct. of the last IFT, and as such, will provide a greater output from that IFT compared to the output that would be obtained if that same IFT fed a simple diode detector.
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*** Al is referring to the HBR 16 receiver here.