Actually, they do seem to be at their limit. There have been articles about this (which I merely glanced over). Scaling up manufacturing for vaccines, especially new RNA based ones, isn't something that scales infinitely with money. Not in the short or medium term, at least. In some cases, scaling up required downscaling of current production.

Searched for the well written article I've seen, to link it here, but I'm only getting SEO bullshit.