This comes down to a common problem with zoos, and that's the disconnect and/or conflict between what is best for the population and what is best for the individual animals. From a purely population management stand point, you're absolutely correct that non-reproductive animals don't "need" to be at these breeding facilities. However, that doesn't mean that these zoos, in conjunction with the SSP, haven't decided that staying at their current facilities is in the best interest of those individual animals. It's a relatively common thing for zoos to have to juggle, and is sometimes quite difficult (especially when dealing with a high profile animal), as oftentimes what is "best" from a population management perspective isn't what is considered "best" for the individual animals. Oftentimes, when this is the case, there isn't really a "correct" answer of which to prioritize.
Furthermore, it isn't like Columbus or Fort Worth are at full capacity either- so it isn't like them being there is harming the population, even if it isn't absolutely necessary. There'd be a much bigger problem is, say, Columbus wasn't attempting to breed their elephants because of housing non-breeding individuals, but we all know that isn't the case.