Transferring bags between identical planes will decrease risk but it won't eliminate it. Unless the same people are transferring (and hence the same bags) then the number and size of bags is going to change.
Presumably people are transferring to the new plane from many different flights, flights have varying numbers of people, people have varying numbers of bags, and bags vary in size.
For example, a few flights into Miami may be only 1/4 full of people but they are 1/2 full of bags because the Miami flyers tend to carry large gear such as golf clubs and scuba gear. If you transfer those people onto a flight to the Bahamas, along with a few folks from other flights, then you might run into a problem.
Presumably people are transferring to the new plane from many different flights, flights have varying numbers of people, people have varying numbers of bags, and bags vary in size.
For example, a few flights into Miami may be only 1/4 full of people but they are 1/2 full of bags because the Miami flyers tend to carry large gear such as golf clubs and scuba gear. If you transfer those people onto a flight to the Bahamas, along with a few folks from other flights, then you might run into a problem.