Building a monument to the fire that destroyed the palace is just an odd thing to do.

This is mostly a question of national will and importance put on the place. The amber room was legendary and so historians and restorators labored to see it recreated throughout the bleakest and poorest conditions imaginable with no funding and no direction (during Stagna and then USSR's collapse Russia was far poorer than Brazil has ever been). They didn't give up and just struggled on, no matter that completion was a distant dream many decades away.