A pull request is very much a proposal: It is a proposal to make specific changes to the code-base. The developers are not forced to accept it in any form, and discussions can take place in the pull request, should the developers (or third parties) not agree with (the exact form of) the proposed changes. Which is exactly what happened in the systemd pull request, to the extent that the actual developers had to lock the thread.
In the case of systemd, the "someone", or rather the "someones", who accepted the pull request also included the lead developer on the project, namely Lennart Poettering. Who else do you propose should decide what pull requests and other proposals to accept?
It's not just server-side: A lot of fingerprinting happens client-side, for example using a canvas to check what features your graphics card supports. You can see this in action via services like https://coveryourtracks.eff.org/ or https://amiunique.org/