Maybe I am missing something but a 0.4% purchase doesn't seem too significant to me.
It's not just .4%. It's a total of 15.1%. Their initial 14.7% purchase plus their affiliate's .4% brings them over the 15% FTC guidelines. More paperwork, etc., etc., etc. Potential delays, etc., etc., etc.
So, regarding the above post by Nyx, that extra .4% is actually a really huge deal in the business world due to the threshold it crosses.