And also don't forget that for many, many,
many people, Kontakt acts as a hub to all their sample library. Simply because there's so many libraries available for it. Every new HISE library is a separate plugin (to my understanding - do correct me if I'm wrong), which eventually would (and I assume will) bloat everyone's plugin lists in DAWs, etc...
Also, try doing bigger libraries (dozens of thousands of samples in a single instrument, lots of groups, modulation and FX going on), then tell me how HISE fares.
Not to mention it has a proper WYSIWYG GUI editor and debugging tools.
Kontakt also has debugging tools (Creator Tools).
Kontakt might be more mainstream
"Might"? It has a huge number of unique installs in the world. People love buying Komplete because of all the goodies, and all the extra available 3rd party stuff for Kontakt doesn't hurt.
if you really have to use some of the built in effects that HISE doesn't have, or time stretching.
Or some of the actual KSP functionality, like the recently added user zones and drag&drop samples directly on the GUI, MIR functions, XY pads, dynamically reordering FX without needing to resort to C++ (according to documentation I found you have to do this if you want that in your library?)... etc. Or use LFOs that go above 10 Hz without resorting to the source code of the sampler or scripting your own, heh...
Yeah, I know I'm biased. I have every right to be.