I don’t think that the resolution was an attempt to justify the price. If that was the case, why go
down in resolution from what’s available? Maybe if they were selling a 9k I would buy it.
Based off some back of the envelope math I did a while ago, I think Apple decided that 6k is the maximum usable resolution for a desktop monitor. At reasonable viewing distances you should be able to tell the difference between a 4K and 8k monitor, but you won’t be able to resolve every single detail of the 8k, hence 6k.