There are several considerations here and some design choices.
As stated, one reason for attenuation is to stop the capsule overloading the impedance converter electronics and is usually done by interposing a capacitive attenuator between capsule and FET input.
Another reason is because capacitor mics generally have a high sensitivity, especially LDCs typically 10X, 20dB hotter than the average dynamic. Most budget mixers and AIs don't have their own input pads these days and so the mic could easily overload some AIs even with a loud singer. Some budget mics do this by cutting the output level but an input, capsule pad is vastly to be preferred.