DarTZeels for sale

DarTZeel power amplifier and recently the DarTZeel preamplifier are becoming two "cult" units within the world of audiophiles. I suppose there aren't many units sold because of the steep prices. So I wonder why there are a few DarTZeel units for sale in the used market within short period, not only the well known NHB-108 power amplifier but also the less well known and quite rare NHB-18NS preamplifier. Are those DarTZeel owners looking for other "flavour", for example tube amplfiers? Have they bought their DarTZeel unit(s) only for some extended home audition? Have they replaced their speakers with some hard to drive ones that require lots of power (that the DarTZeel could not deliver)?
PS: I've always thought DarTZeel buyers were people who want to keep their amps for life.

Chris