The only reason they need to be monoclonal is for drug safety regulations. It's easier to estimate efficacy with a drug of known composition, and safety is much easier too because immune responses to different proteins are tricky to predict.
With a polyclonal, manufacturers would need to prove safety on every single antibody and guarantee composition of the mixture.
Does it really matter?
Well, most of the countries impacted by ebola are quite poor, but I think even ignoring humanitarian concerns, it's probably in wealthier countries' best interests to pay for it strictly from an epidemiological perspective
Plus, also incentives research.
One thing I've often said about infectious disease epidemiology is the Bush Doctrine ("We fight them over there so we don't have to fight them here") is terrible for insurgencies, but excellent for microbes.
Its good that it exists but it might be very expensive to use it across a broad population. Unlike the older pills that were expensive due to patent exclusivity, here fundamentally each pill is more expensive to make.