Why did allied forces find so much destruction when they finally reached germany?

During WW II when Allied forces entered Germany the cities like Berlin, Frankfurt, and others were heavily destroyed because of the ongoing bombing by U.S. and British at day and night. Most of the factories and the cities were destroyed.

German SS Units also played a role in damaging bridges, junctions, roads, ports and any other structure as much as possible that could delay the Allied forces in entering cities.