Maybe one reason to build such a DDR Disneyland is to show how the life was in DDR-times.
But I think main reason is to make money. So the target group are not the germans but the tourists who are really fascinated to see all these DDR things.
Its like the time when I lived in Berlin and the wall came down.
Every tourist wanted to buy a stone, which was cut out of the wall. And the clever germans sold them every stone they found with some colour on it

If all these "original parts of the wall" would have beeen put together we would be able top build 2 or three walls around Berlin

But tourists are nice - they buy everything and gibe money for every nonsense - like Kuckucksuhren or rare real animals like the bavarian Wolpertinger
So why not offering them a DDR Disneyland to spend there the money ?