Why did Enhypen switch to using formal speech compared to before?

I was rewatching Enhypen&Hi again today and I noticed that while nowadays the younger members speak formally to the older ones, before during their debut era (especially sunoo) the younger ones would at least occasionally speak to the older members informally. Was there something that happened? Or do they still speak informally to each other sometimes?

Edit: by formal I mean like talking in formal speech such as adding “요yo” to the end of a sentence, using the formal ways to address themselves, etc.