People with low vision, for example, comprise a large percentage of people with visual impairments. While equivalent alt text is an elegant solution for blind users, mobile users and others who entirely remove or bypass images, for those with low vision there can still be issues with images of text. I believe the intent of this checkpoint is just that – a checkpoint, an invitation to consider that text is still the most easily personalized and reconfigured means to convey information. There are, as you noted, some good reasons to choose images over text, but I guess I would say that if WCAG2 is encouraging anything it is to think twice about it.