It's about normalization. We've come to accept Bridget for what Bridget is, and to have that acceptance jarred by such a stark shift is disconcerting, taking us out of the "comfort" zone we had established through exposure. Perhaps it's the fear that getting used to Bridget as a full female would cause a renormalization once Bridget's true form is restored.
Put simply, we can't bear to get used to it all over again.