Because it's distinctive. It's common for people to hate an architectural trend, that has only recently fallen out of vogue, only later to come to admire it.

Shouldn't that be a matter of documentation in the first place instead of just keeping structures indefinitely?

It reminds me of the Metropolitan Sepulchre plan in the 19th century (https://en.wikipedia.org/wiki/Metropolitan_Sepulchre). While they went with garden cemeteries instead I believe the important point is that cities are for the living and the now and not the past. I personally think that there may be a value to keeping the old around but just mere archivism shouldn't be a reason. If people actually visit it frequently enough certainly keep it but if it is just for the information, we have books for that.

First I've heard of the Metropolitan Sepulchre. I very much enjoyed the link.

    Shouldn't that be a matter of documentation 
    in the first place instead of just keeping 
    structures indefinitely?

There has to balance between razing the ruins of Pompeii, and turning every modern strip mall into a heritage site. Where that balance ought to be is beyond me. Who knows what will interest future generations?

    we have books for that.

I don't know if books are a satisfying substitute. Down the road, when VR is higher quality, that would probably suffice.

correction: I've never heard of the Metropolitan Sepulchre