They did that to Parsec. Their SDK was once an openly accessible and amazing alternative for Steam Remote, which (In my experience) worked better and was easy to integrate into Unity.
Then Unity bought them, closed-sourced, and if you want access to the SDK, you have to ask for it and they have to approve it.
We tried that three years ago, mentioning that we're just a team of students working in school on a two-player only coop project that could really use a multiplayer we can't implement.
This is their response, and I'm still salty about it to this day:
Thanks for reaching out about Parsec! You mentioned in your comments that you were interested in SDK. SDK starts out at $1million. I think upgrading to our Teams plan might assist with the lag issues you're experiencing with your team.
Our Teams subscription starts art $35 per user.
Please let me know if you have any further questions you have.