There seems to be some general pattern here that you can find pretty often in "dev war stories" contexts:

(1) We're a small startup/new product team/etc, let's just build the MVP and keep everything simple!

(2) Now we're not small anymore and suddenly have all kinds of nonfunctional requirements we never imagined before! But our simple architecture from before is making everything a pain now!

The natural instinct is then to compromise on the "simpleness" of the first prototype and already try to anticipate all the scaling and nonfunctional requirements that might come later - but that rarely seems to work, as you can't really how (and if) the project will grow.

Seems to me, the real question here is why those teams are still using the "MVP" code even after being well inside the "scale up" phase. Shouldn't this be the point where you gradually migrate to a codebase that is more manageable at scale?

When you first introduce the idea you'll find a bunch of people think decisions are Reversible which are not, as you say. And the flip side of Reversible decisions is the Last Responsible Moment, which runs afoul of Hofstadter's Law, and people wait until halfway past the last responsible moment.

The key to reversing a decision is getting over Sunk Cost, to start thinking of some code as scaffolding. Scaffolding allows you to get on to other work and then remove it after, because it's either not needed or the 'real' solution has been installed. People get defensive when you propose to rip out their code. Hey that code made us $250k at a time when we were about to miss payroll. Yes. It did. Thank you for your service. But now it's costing us $30k a month and that shit needs to go.

Getting people to figure out that if a decision is important, making it later is actually the sane thing to do, is a challenge. Because many people's intuition is that we should put energy into this now while it's fresh and we have abundant energy. We can 'solve' it and not have it dangling over our heads. But we don't know the right answer yet. We don't know the strength of our tools or the expertise of our coworkers.

The product roadmap is now and has ever been complete bullshit. Refactoring teaches that you amortize rework across all new stories. That's just how it goes.

(And everything should be in GMT unless you can literally point me to a several hundred page treatise on why another time zone is the correct one. Yeah I've worked west coast places that got bought by NY or Chicago companies and it's a clusterfuck if you both didn't use GMT)