[CrimpJiggler]

I've read the explanations of crystal field theory and ligand field theory in my inorganic chem book and organometallic chem book and learned a lot but I still don't have a complete picture in my head of how it all works. Lets say I have a Co(III) ion. Taking the destabilisation of the s orbital into consideration, this is a d6 metal ion. Why do 6 ligands bind to this ion? I've heard of the 18 electron rule and can see that 6 ligands will donate 12 electrons which will add up to 18 but this doesn't explain it to me. Before crystal field splitting, 4 of the degenerate d orbitals will be occupied by a single electron and the fifth will have a pair. Why do 6 ligands bind to this ion and form an octahedral complex? How do they do this? I read before that ligands donate their electron pair to an empty d orbital but this is obviously not the case here since there are only 5 d orbitals and all of them are at least partially occupied.