They likely signed non-disclosure agreements, breaking one of those could be a career-ender.
NDAs will be void in the future when people wrestles back control from the corporate elite controlling so-called democracies
ndas aren't legally binding in the UK. what they have signed is non-disparagement agreements (not allowed to publicly disparage the company)
If it's juicy enough presumably they could be an anonymous source for some journo. Which would still be breaking the NDA but good luck getting anywhere with that.
If they’re not willing to break an NDA for it, it can’t be all that serious.