^^^^ What you've suggested above is certainly an aspect of this. They have been building more multi level units at Hobsonville and Ellerslie and its a tough sell when development is going on all around you. SUM's holding costs are not huge as their recent 7 year bond offer clearly showed pitched at just 4.2% per annum. They'd probably rather sell units at premium prices when the multi level construction is complete than discount them to shift units in the middle of a Sahara sandstorm.
On another topic its good to see them buying a decent chunk of land in the fast growing Papamoa area. I for one am happy to see them buy there rather than expanding in Australia at present what with their falling real estate market over there and Royal commission of enquiry ongoing. https://www.nzx.com/announcements/324901
One thing you have to take your hat off to SUM is when they say they are going to build XYZ units in any given year they do exactly that, they have never once failed to meet a build number target since listing nearly 7 years ago. That's no easy feat in this construction market and their development margin has shown excellent growth over the years. I think I will hang in here and trust management know what they're doing. I think they have earned my trust over the years.