Apple sued DRI, which resulted in the crippling of GEM, the glaring one I remember were static windows. You heard that right, windows were not resizable but had fixed screen locations in the PC version.

Thankfully Atari licensed GEM for their 68000 machines before the lawsuit, and wasn't affected by these changes. The Atari ST (Sixteen/Thirtytwo) was very Mac like at the time. It even ran the Mac OS from Apple ROMs (Spectre 128 and Aladin) on its much cheaper hardware.