In Japanese, saying 「なる」 is preferred over saying 「する」. Using 「する」conveys that ①has the speaker's will; Using 「なる」 conveys that it is not the speaker's will but something that naturally happens, that things are in such a state.
For example, in a situation where a customer is smoking at a non-smoking restaurant, how will the restaurant tell the customer to stop smoking? The person who decided to ban smoking at this restaurant was the restaurant's own person, the restaurant must have banned it according to their will. If so, saying 「ここは禁煙にしております」sounds natural. But this way of saying 「〜にする」, ②as written above, conveys the speaker's will very strongly. In this situation, the opposing will (note 1) to the other person's action of "smoking" is expressed too strongly, which can result in the guest's anger. On the contrary, if you say 「ここは禁煙になっております」, it turns out it has nothing to do with your will, it's simply conveying the restaurant's rules, thus saying what you want without creating a confrontation.
Thus, Japanese people cleverly use 「なる」to avoid antagonism with others. 「する」and「なる」on the surface are only one letter different, but in communication, it is a huge difference.
(note 1) 対立する: both sides stand in opposite positions.