One challenge is that they have a ton of usage under their free tier, especially by free and open source projects which have near zero budgets. Its an artificial economy of projects that cannot pay for their own usage.

Another challenge is that the GitHub Actions paid tier is already very expensive, the quality of service is poor, and they have major security challenges. They could load shed by raising prices, driving customers to other platforms, but they already charge 10x what others charge (https://runs-on.com/pricing/#runner-pricing, https://www.ubicloud.com/docs/about/pricing). Anyone using GitHub Actions at scale would be somewhat price insensitive already.