Saved them money on licensing their existing font, so why didn't they just move to another cheaper or free font?

Because those fonts have different metrics, so they wouldn't have been drop-in replacements, they would have had to re-do all of their branded media.

Loose programming analogy: The free replacements had a slightly different "API" (metrics) that would have required adjusting hundreds or thousands of "call sites" (media using the font), so instead they made their own "API-compatible" (metrically compatible) replacement that dropped straight in.

This is all covered in the documentary short about the font.