Comment by Jorchime

I think it is because of what is described through Conway's law: https://en.wikipedia.org/wiki/Conway%27s_law

    Any organization that designs a system (defined broadly) will produce a design whose structure is a copy of the organization's communication structure.[2][3]
    — Melvin E. Conway

The problem isn't necessarily software itself, but how we organize people (more than 2 or 3), how we communicate, how we mirror operations, expectations, etc. in software.

Scaling sustainable software feels like an "unsolved" Problem, because the society hasn't figured out how to organize better.