Why twelve point Times New Roman isn't always a good idea

Why twelve point Times New Roman isn't always a good ideaI am currently sitting in the very back of a conference room with about 170 attendees. Up front is a good speaker, except for the fact that he uses slides with a ridiculously small font.

Why do people write so much anyway? There is no call for all this insane amount of writing on a slide. Give me an illustration please, don’t kill me with tiny words!