We simply don't want to care about legacy OpenGL.

All supported platforms also have support for OpenGL ≥ 3.2; it would
complicate the internal code; and would force us to use legacy GL
contexts internally if the first context created by the user is a legacy
GL context, and disable creation of core-3.2 contexts after that.

We will need to fix all our code examples to use the Core 3.2 profile.

https://bugzilla.gnome.org/show_bug.cgi?id=741946