Before the compiler had const generics at all, array implementations were all duplicated for [T; 0], [T; 1], ... [T; 32] using macros.
Now that we do have const generics, those have been consolidated with const type parameters for the length. However, as that feature is still unstable, we want to have an easy way to go back, so we keep the former limit using LengthAtMost32. If we need to rip out const generics for some reason, we still can.
Eventually, this should be opened up to all array lengths.