When you're making a work of art (such as a game) you don't just want any old font, you want one that serves a particular aesthetic purpose.
If you've picked a typeface, and designed other UI elements that look good in conjunction with it, but suddenly that typeface becomes unaffordable, then you have to do some work to find an alternative that's still acceptable.
In particular, game UI tends to be designed around the particular dimensions (metrics) of a font's characters. So a string of text whose size is "just right" in one font might look too big or too small in another, even at the same nominal font size. And this can affect many different pieces of text throughout a game.
If you've picked a typeface, and designed other UI elements that look good in conjunction with it, but suddenly that typeface becomes unaffordable, then you have to do some work to find an alternative that's still acceptable.
In particular, game UI tends to be designed around the particular dimensions (metrics) of a font's characters. So a string of text whose size is "just right" in one font might look too big or too small in another, even at the same nominal font size. And this can affect many different pieces of text throughout a game.