DirectWrite doesn’t apply subpixel anti-aliasing by default [0], and an increasing number of applications use it, including Microsoft Office since 2013. One reason is the tablet mode starting with Windows 8, because subpixel ClearType only works in one orientation. Nowadays non-uniform subpixel layouts like OLED panels use are another reason.

[0] https://en.wikipedia.org/wiki/ClearType#ClearType_in_DirectW...