I really hope the privacy-conscious people downloading this aren't just downloading these binary blobs and instead compiling it from source. Especially after seeing this disclaimer on their download page:

>>>IMPORTANT: These binaries are provided by anyone who are willing to build and submit them. Because these binaries are not necessarily reproducible, authenticity cannot be guaranteed. For your consideration, each download page lists the GitHub user that submitted those binaries.

Couldn't they (or someone) set up a Github Action to compile the project on every release?

GitHub Actions free tier comes with ~34 hours of free compute time with 500MB storage. Pro comes with 50 hours and 1GB. Enterprise comes with much more. Building on Windows or macOS divides those compute rates by 2 and 10 respectively.

For a project with frequent point releases, building Chromium via GitHub might require a monetary commitment.

Has it changed? It used to be unlimited for open projects.

I wasn't aware it was ever free for open projects. Reading this page shows that you're right[1], public repositories can use GitHub Actions for free.

[1] https://github.com/features/actions