Because 0CC-FamiTracker provides a better workflow, atleast for me.
Making wavetables and them being more easily switchable (basic wavetable sampling made more easy as well) and being more organised the way FamiTracker does it is more convenient, having arp schemes and grooves are my most important reasons.
Besides, Deflemask misses some functions or are broken. Take the noise volume differences: I know Huzak makes up for that difference and corrects it, but maybe I want to have it louder at a certain point in a song. Elmer mentioning missing noise frequencies and no switch mode between wavetable and noise (though Delek said he added that).
While reading documentation there's apparently a global- volume and -stereo volume function there.
More sound engine options are also nowhere or badly to be seen in Deflemask (sample rate, and the buffer option is better in FamiTracker).
More convenient controls, echo buffer... I think I've said reasons enough.
No offence, I'd use Huzak for with Deflemask, but I hope you can agree that a dedicated tracker specialized for a sound driver would eventually be the best. 0CC-FT is also opensource, so there's way less hassle figuring out the inner workings of the program.