I don't think it's fully available, so it's rationed for high risk cases. And it's expensive (much more so than a vaccine, you need an IV and to go sit in a hospital room for awhile)
The technology to make monoclonal antibodies is simpler than that for mRNA vaccines.
> That's also the reason they tend to be so expensive
Economies of scale play a big role. At similar scale mab should be cheaper than mRNA.
It’s more mature technology, but unlike the mRNA vaccines it’s not cell free and as a result is harder to scale up. At similar scale mRNA will still be cheaper; that’s one if mRNA’s biggest selling points.