If they shipped, gained customers and allowed the company to make money, they did their job.

I have to ask. Does this mean that maintenance is always someone else's responsibility and never someone's responsibility directly?

Maintenance is not a “problem” even if I am the maintainer or in my case, the “rearchiterer”. It’s what they are paying me to do. What a company needs at one phase of its existence is different than at another phase.

It would be just as wrong for me to come into a company at the beginning of its existence when they are just trying to go from 0 to MVP and worry about unit tests, branching strategy, and “process” as it would be to promote the pioneer to a team lead.

Interesting analogy, and I would agree if the developer is intentionally concealing their actions to escape consequences.

However, the situation is more often someone inexperienced doing a bad job, or someone experienced doing a bad job because they're crushed by unrealistic deadlines, or someone cutting corners intentionally because the company is in a do-or-die situation. None of these are immoral, but result in the same outcome.