Why does Cinnamon forces 96 DPI as GNOME 3 does? This issue has ben a major source of criticism for GNOME 3 and the approach is widely considered to be a wrong one.
It even breaks the scaling of Qt applications (not sure about GTK ones). For example, just open scribus and create an A4 document. When zoomed to 100%, the on screen page size differs from the real one. But it works well in other desktops like Xfce or KDE.