If bullets with a high BC kill just as well as others, why in the wide wide world of sports would you not use them?
There are multiple reasons one might choose a lower B.C. bullet:
1. Cost
2. Accuracy
3. External ballistics
3. On-target performance
The first two are pretty self explanatory.
External Ballistics. A higher B.C. does not guarantee a flatter trajectory. Often the higher B.C. bullet weighs more, starts out slower and, in terms of trajectory, retained energy and velocity, may not overtake the bullet with the lower B.C. until way past where the shooter is willing to take a shot - if ever.
On target performance. Bullets with different construction often behave very differently after impact. Those that essentially self-destruct can provide DRT results but I don't trust them to penetrate on bad angles. Bullets that hold together and "kill just as well as others" can be generally be relied on to provide better penetration on bad angles. Bullets that come apart can destroy a lot of meat unnecessarily - bullets that hold together often do less such destruction.
Every hunter has to choose their bullets. Some put little or no thought into the selection process other than cost. Others put a lot of thought into it and select based on a combination of factors. Most people are probably in-between those extremes. You're probably aware I prefer to plan for the worst and work for the best and that, accordingly, I prefer bullets that hold together, even if that means a lower -- but high enough -- B.C.
