Why is a git 'pull request' not called a 'push request'?

If you have a code change in your repository, and want to move it to a target repository, then:

• "Push" is you forcing the changes being present in the target repository (git push).
• "Pull" is the target repository grabbing your changes to be present there (git pull from the other repo).

A "pull request" is you requesting the target repository to please grab your changes.

A "push request" would be the target repository requesting you to push your changes.

When you send a pull request, you're asking (requesting) the official repo owner to pull some changes from your own repo. Hence "pull request".