Ann: Tawana & Alliance to Merge and Capital Raising & SIA, page-404

Off the top of my head, I could suggest;

Because the drilling was delayed
Because the assay results have been delayed
Because they have limited staff to work on it
Because their attention has been on expansion planning
Because their attention has been on mine planning to feed the accelerated expansion
Because their attention has been on the merger
Because their attention has been on the assets being spun out
Because they were going to be cash restrained prior to the CR, and have now decided to do more drilling ASAP and deliver a more comprehensive update when it does come out
Because they need to go bigger than originally planned to justify to the market and the ASX why they're building a second DMS already (assuming the planned updated reserve was only enough to feed one DMS for 7-10 years)

And most importantly:
Because it doesn't matter a rat's fluffy little rectum if the update comes out in April or May or June, as long as it is done right?

Mix and match as you wish.