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because you probably compiled qjackctl yourself without ALSA API support?

this is most probably the same reason why you get the ALSA tab grayed out on the other topic.

if your on debian/ubuntu based distro, please install libasound2-dev package and build and install again from a clean source;
if you're on fedora, install alsa-lib-devel; on opensuse it's alsa-devel.

in summary you have to make sure the ./configure step reports this line:

  ALSA MIDI Sequencer support  . . . . . . . . . . .: yes

hth.
cheers