A good chunk of that is that people had finally gotten a delivery mechanism to work in the past few years. The "for a decade" is misleading, because a decade ago it was an interesting idea nobody had gotten to work in a way that was useful. 2020 it was something with good promise and product development under way that could be sped up massively with more money and acceptance of it being a gamble.
This feels like a post-hoc rationalization to me. Of course it was less ready, and then more ready. But exactly how much of a gamble was it?
The upside is immense even considering just existing diseases, but we are really bad at pricing things that improve the status quo vs prevent bad things.
The theory, assuming a delivery mechanism is found, is rock solid---"if not when"---and I therefore wouldn't call it a gamble.
On the other hand, I don't know enough about the biology to speak to the difficulty and uncertainty around delivery mechanisms. Can we get more info on that? I suspect it wasn't too uncertain, though "oh, we change this base pair a bit and the immune system doesn't care" does seem like a relatively unplanned discovery.