I think supply could be down because many of the higher end houses and apartments built in Dublin over the past few years have tried to revert to renting instead of selling due to little interest at the asking prices. I think they saw the asking rents for apartments in e.g. Ballsbridge and decided they could achieve those rents as well. If they actually walked down there, they would have noticed that many of them were still vacant.
As an example, back in January, the developer of apartments at Deerfield in Ballsbridge returned all booking deposits due to lack of buyer interest where two beds were priced at up to €1.3 million and he stated “uncertainty owing to Brexit has a hand to play in the sluggish sales market.”. Article link here: https://www.irishtimes.com/life-and-style/homes-and-property/plan-b-for-d4-boutique-apartments-as-buyers-become-renters-instead-1.4161644
On MyHome.ie today, there also appears to be c. 108 houses for sale in Dublin that have asking prices between €1m and €1.25m or c. 345 houses with asking prices over €1m.
Another possible reason could be that the number of properties for sale over €1m has fallen due to previous asking prices falling from over €1m to below €1m e.g. from €1,150,000 to €995,000 to reflect the changing market?
I’d also assume a lot of sellers may be holding back until they get a better feel for where the market is heading. They may soon take Glenveagh’s view and re-list their homes in the near future at lower prices to reflect this changed market.
I’m sure there’s many other reasons, but I don’t believe it’s an actual lack of supply at the €1m+ price level.