We used to have a lot of people like this running businesses in the US before roughly 2012, but white (and black) hat hacking began spreading quickly and made generally short work of the problem.
We employees of the acquired company discussed the emails in Slack: we were sure that these emails were legitimate, but acting on them would have broken our security policies, so we all decided to all report them as phishing attempts. We understood that we were engaging in malicious compliance, but our actions were also a best practice, so we couldn't technically be criticized for it.
After a while of this, execs at the parent company would send out sometimes exasperated-sounding emails ahead of time, alerting us to the email that we should expect to receive and how they wanted us to respond. Of course, that led to discussions of how we know that that pre-email emails were legitimate. After a while, we all lost interest in this malicious compliance and adopted the much laxer security culture of the acquiring company.
The absolute last thing anyone competent does is train employees to receive communications like that in email and follow them. If they'd asked for 3 minutes at an all hands to prep employees, or announced in slack, or something similar then ok. Or some out-of-band announcement that this was legit.
There's almost a catch-22: setting good, effective policies tends to involve a lot of telling people "no". And it's hideously difficult to do that without ruffling the feathers of people who control promotions.
It doesn't make any sense to me because it's expensive to make sure your company's services are secure, but it's also expensive to not be secure. Perhaps it's less expensive to not worry about it because the loss-of-customers impact on revenue are still under the cost of doing it right. If that's the case it's a sad state for all of us.
I don't know of anything that can convince a group of leaders making money and doing fine to change besides fear. Perhaps the US with its lawsuit-happy culture helped propel such changes more quickly than in Western Europe.