This times a thousand!

In the years before VMs, containers, and locked dependency manifests, it was essentially impossible to get repeatable builds. There are still a lot of hurdles and gotchas, but we can at least get a rough approximation. The idea that some other pre-2010 dev team was going to be able reliably build your thing from just raw source code, and have it closely resemble the thing you built—it was a delightful fantasy. Escrow was a sales and legal "don't worry we have that eventuality covered!" CYA and emotional de-risking move, not a practical expectation of ability to build from scratch.