They didn't really have a hole they had to fill... It's not like there was a big wall with nothing on it and had no clue what to put on.
They just had some memory place left and decided to put something on the wall that took more memory than a standard texture.
And for the in-world interpretation, you might see it as some inspirational propaganda made for Sligs, which was a huge failure because most of them were sleeping in that facility anyway. (if my memory serves right)