It has to do with the laser being worn out. This method slows the CD motor down, helping the burned game be read. People have done it by pressing firmly on the lid, which puts pressure on the top of the spindle, causing motor strain. Some people put the whole unit on its side. Other methods include adding two CDs to the spindle, obviously with the data one on the bottom, to add the strain.

There is also a 3D-printed weight disk people use at https://www.thingiverse.com/thing:4838168 .