The answer is economics. Amplifiers are voltage sources and practically all speakers are designed around being powered by a low impedance voltage source. Change the output impedance of an amplifier and then it sounds better with some speakers and worse with others. The industry is not going to get together and do an Avalon-Spectral-MIT marriage of specification. The ones making current source amplifiers are mostly the ones making active speakers. In short, to optimize a current source amp you must convince the speaker maker to tailor his specs to your amp. Not gonna happen.
Are all amps being built wrong?
The power amplifiers that drive our loudspeakers are mostly built as a low impedance voltage source. They have always been ... but why?
Loudspeakers have a (greatly) varying impedance over the frequency range. A current drive amplifier would eliminate the issues that stem from this varying impedance, and at the same time make discussions about esoteric speaker cables that strive for optimal R, C, L superfluous. Although there still would be these un-measurable ’this (very expensive) cable sounds better’ debates and opinions ... and that’s OK, that’s part of the fun. :)
So ... why are amplifiers not built as a high impedance current source?
This is an interesting read: https://www.current-drive.info/
Loudspeakers have a (greatly) varying impedance over the frequency range. A current drive amplifier would eliminate the issues that stem from this varying impedance, and at the same time make discussions about esoteric speaker cables that strive for optimal R, C, L superfluous. Although there still would be these un-measurable ’this (very expensive) cable sounds better’ debates and opinions ... and that’s OK, that’s part of the fun. :)
So ... why are amplifiers not built as a high impedance current source?
This is an interesting read: https://www.current-drive.info/