Collectively their creator/owners will be paying thousands of dollars/month for their fonts. Something you’ve correctly assessed that a very low number of their viewers will notice or care about.
Nebula can make one upfront payment (likely less than a single months font foundry payments for their owners), and give the creators absolute certainty that the created font is free forever, no matter the viewing platform or medium.
Seems like a decent place to allocate some idle cash.