From my understanding, the LOI isn't necessary if you know the school isn't going to drop you. It binds the player to the school, so that if he breaks it and decides to go elsewhere, he has to sit a year. Essentially, it's the same as enrolling in the school, from the player's perspective.
Obviously, the plus side for the player is, if you sign the LOI, you lock in your scholarship spot for that year. However, if you're an elite recruit, you have no need to lock in your scholarship, because the school isn't going to drop you. Therefore, why sign a contract binding you to a school, if you don't have to do so to reserve your spot?
I think the trend is the result, in particular, of the practice where coaching staffs have worked out deals to wait and not let their assistants leave until after Signing Day, and often the player signs with a school only to find out that the guy who convinced him to sign is not going to be there in the fall. If you have the leverage to hold the school accountable, why not?
Yancy was saying (I know, I know) that Malik is considering not signing an LOI. Take that FWIW, but he really doesn't need to. Just sign scholarship papers, which obligate the school to you, and enroll when it's time.