You have always been allowed to have arrays longer than 32 elements, but dealing with them used to be hard. Beyond the Copy trait, which is a compiler builtin, many traits weren't implemented for arrays with more than 32 elements.
And the feature is still limited. For example, legacy users like serde still can't switch to the new const generics based approach, because of the same issue that the Default trait is facing. Both traits could be using const generics, if they were allowed to break their API, but neither want to, so they are waiting for improvements that allow them to switch without doing a hard API break.
The first such change was implemented in 1.47.0 in 2020 where a bunch of traits were made work on all array sizes: https://github.com/rust-lang/rust/blob/master/RELEASES.md#ve...
It took a few releases, until 1.51.0 in 2021, until custom traits could be implemented for arrays of any length: https://github.com/rust-lang/rust/blob/master/RELEASES.md#ve...
And the feature is still limited. For example, legacy users like serde still can't switch to the new const generics based approach, because of the same issue that the Default trait is facing. Both traits could be using const generics, if they were allowed to break their API, but neither want to, so they are waiting for improvements that allow them to switch without doing a hard API break.