Your last part there is wrong: as covered in many comments here, the A380 is still selling, in fact to the same carrier that's not renewing the leases on these early models. So it does still have a niche that it excels at; the problem is just that the early models have too much weight compared to current models.

This isn't about the A380 vs. other models, this is about old-A380 vs. new-A380. I was just asking why it wasn't feasible to retrofit the old ones to match the specs of the new ones, which these carriers do want and are buying. I could understand if we were talking about cars, where there's a well-tuned assembly line and it's almost never cost-effective to retrofit, and the unit cost is actually shockingly low when you consider the complexity and cost of components, but large aircraft aren't like cars. (Aircraft assembly plants make a few dozen a year, car plants make hundreds of thousands.)