K1R, as its name suggests, is primarily focused on restoring content that was cut from the game. I think the primary examples are an additional level of the Black Vulkar base on Taris and the Pazaak tournament on Manaan. It does include some bug fixes, but that isn't why people use it.
K1CP, on the other hand, is exclusively focused on fixing bugs and other issues. It makes the occasional quality-of-life change, but for the most part it is intended to be fairly seamless and unobtrusive.
As K1CP has expanded, the scope of changes it makes to various modules mean that it is no longer considered safe to use with K1R. There are certain types of changes that can't be integrated with TSLPatcher. Hard conflicts like two mods overwriting the same script that would require manual merging. I'm sure with some effort they could be made compatible, but nobody has expressed any interest or volunteered to create such a patch that I am aware of.