That answers the question why robustness will dominate the population once it is evolved.

I don’t think it does. It’s a circular argument, which assumes that robustness necessarily guarantees a reproductive advantage. I don’t know why anyone should believe that.

In top of that, it’s not like some organism evolved a robust design in some feature, it’s a question of the discovery of a design principle.

I’m sure none of us have a problem with accepting that explanations should be reasonable. But if there is no reason for it, how can there be an explanation?

How about – robust organisms outcompete nonrobust organisms?
That answers the question why robustness will dominate the population once it is evolved. It does not answer the question why the mechanism got there in the first place.

If organisms evolve robustness, a design principle, I think an explanation is in order.

How about – robust organisms outcompete nonrobust organisms?

These “regulated errors” comprise a novel non-genetic mechanism by which cells can rapidly make important proteins more resistant to attack when stressed.

Robustness is a design principle. If organisms evolve robustness, a design principle, I think an explanation is in order. Why do organisms evolve in such a way that they come to incorporate design principles? Pure luck?