1) Because it can be installed separately, so no need to force using it on everyone
2 ) Because during standby state with AP connected, some things doesn't work (probably, power-saving) and it eats battery a lot. Pali introduced fix for this issue, but it can be installed only (almost) via CSSU, and CSSU devs need more people *without* KP installed use it, to confirm that it doesn't contain any bugs. My personal opinion is, that it should land in CSSU-testing anyway - well, it's testing, after all - but...

/Estel