When you add features such as telemetry, curl calls in install scripts, and in general build on public cloud infra, everything assumes you have internet connectivity. That assumption is so crucial that it is embedded in everything and touches most software components. When you already have an established product, I imagine changing it to remove the assumption without a full rewrite can be tricky.
Yes, agreed, if you build with air-gapped in mind from day one, it should just work.
In our case, we had to unwind a bunch of assumptions baked into modern SaaS: license checks, analytics, image pulls, update pings… even small things like font hosting or third-party embeds needed rethinking.
Not hard in principle, just a lot of invisible cleanup to make it truly self-contained. Learned a ton doing it.