Why not just `scp ~/.tmux.conf remotehost:`?

I can't speak for the parent, but I rarely login to the same remote server twice and don't want to need to set things up and clean them up anytime I do. This is why I try to keep my stuff as close to vanilla as possible. If anything goes wrong on a server and someone sees I have a whole bunch of dot files to customize my config, it becomes a red herring that I have to spend time explaining away.

If only we had ways to automate repeating processes… oh well

No, wanting to keep things vanilla when you're dealing with lots of random servers is a valid concern. Just because you can solve this with shell scripting doesn't mean you should.

You could always copy the config to /tmp and use the -f flag.

Sometimes I ssh into a server as a specific user (e.g. as the "app" user that is used to run a web app), sometimes only root is available (probably not best practice, but it's not like I can or want to fix it myself).

In any case it's not practical to carry your dotfiles everywhere you go. Changes are also a hassle to propagate

Because I'm not the owner of the remote host.