Why do so few low power amplifiers using 300B have balanced inputs?

Most 300b amplifiers are single-ended.

Most designers think that there is no point to adding a balanced input to such an amplifier.

But the fact is there is a way to do it (without an input transformer too) that allows the amplifier to process both phases of the balanced signal.

Any single-ended amplifier can be easily modified to do this without changing the character of the amplifier. FWIW, most single-ended designers don't know this is the case.

Most designers think that there is no point to adding a balanced input to such an amplifier.

What would be the point?

What would be the point?

Depending on the design of the specific preamp that is being used, perhaps less sensitivity to cable effects, less susceptibility to ground loop issues, and in some cases perhaps better sound from the preamp’s balanced outputs than from its unbalanced outputs.

There seems to be a belief among some audiophiles that balanced interfaces can only be beneficial if the internal signal paths of each of the components are balanced. I see no basis for the belief. Depending on the specific designs a balanced interface may provide better results or worse results than an unbalanced interface, even if some or all of the components are not "fully balanced."

Regards,
-- Al