It's not uncommon for a White Paper to be marred by delays – or scrapped altogether. The life-cycle of the Levelling Up White Paper is no different, appearing first as the Devolution White Paper, followed by the Devolution and Local Recovery White Paper until its current form.
When Michael Gove took over as Levelling Up Secretary in September, there was an expectation that he'd shake-up the re-branded Department for Levelling Up, Housing and Communities. The delay to the White Paper in December wasn't wholly out of sync with his reformist character insofar as it has, in theory, given him more time to shape the White Paper in his own image.