The reason for this is player A in these situations is a guy who has never played QB in a pro style offense and is basically going to be a developmental prospect either as a receiver or as a QB.
The player however is seen as having the athleticism to play either position. Therefore he is going to be most valuable to his team in whichever position he can make the biggest impact to the team the quickest.
As a QB this guy will have to be carried on the roster for probably 2 or 3 years without truly impacting the team in any way. After that time he may or may not have developed into a solid stater.
As a WR/KR however the guy can really make more of an impact much earlier. Based on pure athleticism and elusiveness which can be seen from the running ability he has shown he can already produce at least somewhat as a returner and sensationally on screen passes, reverses, and other such plays as well as a wildcat QB. That alone is probably more valuable than the chance that he might become a solid starting QB plus then he has the chance of becoming a solid starter as a receiver. This is a much safer and much more appealing situation for the team as he can at least make some impact right away without really greatly lowering his ceiling potential impact too greatly.