That specific case works. But, it's "yum install nginx" some places. And some package names vary by distribution and even versions of same distro. And there is

That specific case works. But, it's "yum install nginx" some places. And some package names vary by distribution and even versions of same distro. And there is post install configuration that has to happen. And there is coordination with the proxy cluster, the memcache cluster, the db cluster, monitoring system that has to happen. And many sophisticated users will need a custom nginx or extension which requires building locally (and all those dependencies) or private repo. And you're glossing over configuring sudoers so the user you are logged in as can even sudo in the first place. tldr; Provisioning is fucking hard.