I hate to be that guy, but the documentation for AD DHCP goes over this.
It isn’t always Microsoft’s fault when they fail to save their customers from their own stupidity and lack of concern for security.
It is bad that this is the default behavior, but defaults aren’t always defaults because they are the best, they are the defaults that will all work functionally together as long as everything is at default settings.
It is more about making it “work out of the box” with defaults than “making sure it is secure out of the box.”
Frankly, the security of their AD DHCP/DNS is the job of the SysAdmin, not Microsoft. A SysAdmin is supposed to be a professional, so why do they want to blame a third party for their own shortcomings and lack of security conscientiousness?
Nobody is blaming Linus for badly secured Linux servers, or saying the defaults should be more secure.