Maintaining Cybersecurity Insurance is a big deal in the US, I don't know about Europe. So vulnerability disclosure is problematic for data controllers because it threatens their insurance and premiums. Today much of enterprise security is attestation based and vulnerability disclosure potentially exposes companies to insurance fraud. If they stated that they maintained certain levels of security, and a disclosure demonstratively proves they do not, that is grounds for dropping a policy or even a lawsuit to reclaim paid funds.

So it sort of makes sense that companies would go on the attack because there's a risk that their insurance company will catch wind and they'll be on the hook.