If a client has certified a specific Linux distro as an approved platform, that's what we use.

We can either deliver a single executable (Go) or a Python script, as python is preinstalled on their distro.

If we'd want to use Ruby, it'd be a huge hassle of re-certifying crap and bureauracy and approvals and in that time we'd have the Python solution already running.

Without a root account or inclusion in sudoers list, quite hard. There's millions of people that don't control the machines they work and spend most time with.

Significantly harder than doing nothing

Depends on you, your team, your target hardware/os, your project, and many other factors. Considering all of those things, the hurdle of installation might just be too large for it to be worth it.

It's not. This is a non-issue. Every web shop is writing bash to twiddle a build script on servers they also manage, which includes the ability to install any package they want.

How hard is it to install anything? That really isn't the point.

Mitigating the risk of downloading a script from the internet and executing it -- even from a "trusted" website or package manager -- is absolutely a good reason not to use it.