Why would anyone want class AB amp when class A always sounds better ?

The lowest distortion amp in existence is class AB. The problem with this amp is it doesn’t have any low-order harmonics to help mask any inadequacies in upstream gear or the recording. 

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In solid state amps only a handful and in tube only a handful also they are incredibly difficult to make and unreliable due to heat generation because of the 10 percent efficiency. So most of the makers if not all stopped making them.

This statement is false. We've been making class A amps for over 45 years. Reliability isn't an issue- that's an engineering problem, not something inherent in the class of operation. They are more efficient than 10% too- that's about a country mile off as the saying goes.