Why Single-Ended?

It would seem so.

In order to support the balanced line standard:

1) pin 1 is ground, pins 2 and 3 carry the signal
2) the signal occurs between pins 2 and 3.
3) Ground (shield) is ignored
4) the system is low impedance.

Again as I pointed out earlier, most high end audio systems don't do so well with 3) and 4) nor for that matter 2).

If they did though, the capacitance becomes a non-issue in lengths of 200 feet or so (which should be practical in most homes- at my place they are only 30 feet).

So, Again. If the equipment supports the balanced standard, you won't hear the effects of the cable. IOW if you can hear the effects of the cable, its likely that your gear does not support the standard.

I come from the 'pro audio' side. Looking for a reasonably priced ( OK, cheap) 5 channel amp, I couldn't believe that so many 'hi-fi' amps are unbalanced. I've never used a fully balanced topology (may be, probably is, superior!), but I've come to the conclusion that an XLR connector (with a short cable run)  just introduces yet another circuit into the audio chain ( balanced->unbalanced op-amp) which is to be generally avoided, notwithstanding that companies often choose to shave-off a few cents of quality at this junction.

Can somebody give definitions and explain differences  between:
single ended
balanced
truly balanced
fully balanced
differential
differential balanced 
full differential
truly full  balanced
truly full differential balanced

Can somebody give definitions and explain differences between ....

First, keep in mind that these terms are often bandied about in a loose manner, and some are inherently ambiguous. So you may frequently see a given term used to mean different things. And there may be legitimate disagreement about some of the following definitions. But FWIW I’ll give it a shot.

Single-ended: Either not balanced or not push-pull, depending on context. I have interpreted the OP’s question as referring to "not balanced."

Balanced: If referring to a pair of signal lines, the two lines have equal impedances relative to the ground of a circuit, or the two lines are not referenced to a ground. If referring to a pair of signals, the signals have nominally equal amplitudes but opposite polarities. If referring to a circuit or component, the circuit or component processes signals having nominally equal amplitudes but opposite polarities in a symmetrical manner.

Truly balanced: Not a technical term, but sometimes used to distinguish between an XLR connector on which a balanced pair of signals is present, and an XLR connector on which just one signal is present. Also sometimes used to mean "fully balanced."

Fully balanced: The entire signal path of a component is balanced.

Differential: A circuit within a component, or the entire signal path of a component, responds to the difference between two input signals. May also refer to a form of balanced design in which the signal path of a component consists of a series of differential circuit stages.

Differential balanced: Usually used in a loose manner to mean "fully balanced."

Full differential: Usually used in a loose manner to mean "fully balanced."

Truly full balanced: Usually, a somewhat redundant way of saying "fully balanced."

Truly full differential balanced: Usually, a somewhat redundant and clumsy way of saying "fully balanced."

Regards,
-- Al