Well, this way they could install dependencies anyway just automatically, so you don't see them unless you read before accepting the installation. I still can read this:

Install and configure the necessary dependencies
sudo yum install -y curl policycoreutils-python openssh-server perl

And then:

Add the GitLab package repository and install the package
curl https://packages.gitlab.com/install/repositories/gitlab/gitlab-ee/script.rpm.sh | sudo bash

So they do some magic here, the script just installs the repository, so I can't see exactly any dependency they are currently using.

it also wont benefit from updated dependency packages

If they maintain the binary properly, could cause less issues with dependencies compatibility, so it's less pain for the DevOps team, like a container image, just pull the new image and done.