One thing is, as someone who develops cross-platform software, you really want font rendering & unicode support to be exactly the same across platforms, so that users don't have a save file that looks one way when opened on a Mac and another way when opened on a Windows.

This means that you can't use the OS provided facilities (as they all have different metrics) and have to bundle good font rendering engines (if you care about non-us-ascii people) - that means already ~7-8 megabytes at the bare minimum for that.