This website contains age-restricted materials including nudity and explicit depictions of sexual activity.
By entering, you affirm that you are at least 18 years of age or the age of majority in the jurisdiction you are accessing the website from and you consent to viewing sexually explicit content.
That is probably for safety. If you microwave water without anything for it to nucleate on, then it can be liquid above the boiling point. If you then put a tea bag in, it will explode into steam in your face.
That’s really only an issue for microwaves that don’t have the turntable.