Also you can have so few devs when your value is in your network. Most other businesses' value is in their features. We have customers constantly begging for features, so we have to have more engineers to produce more value to our customers.

I believe that the instinct to over-engineer is based in part on bad prior experiences with trying to separate concerns after it's 'too late'. Either your own personal experiences, or those of your mentors.

Lacking any better skills to identify and avoid those problems when they begin, they try to stop it from happening in the first place. Fences get erected everywhere in case they might be needed, and they frequently turn out to be in not quite the right spot or shape. The code becomes coupled to the bad interface instead of to other code, and the fixes are just as bad.

YAGNI in theory is about trying to develop those other skills, but gets twisted into an excuse for bad tech debt loads.

As someone said, microservices is a technical solution to a people problem. Devs don't want to talk to each other so they wall off behind their own API. Boom, no need to talk to each other. Ever. Or is there?

Requiring everyone to talk to everyone so everyone has global context isn't just "devs don't want to talk to each other"; it is actually an information dissemination and coordination problem which scales non-linearly (at least n^2), and needs some kind of modularity to be tractable to normal humans.

Microservices are like modules but for SaaS rather than shrinkwrap, and are where you end up when you follow SLAs, encapsulation of resource consumption, etc. to their logical conclusion.

"Microservices" don't guarantee that everyone doesn't have to talk to everyone. Good thoughtful design is necessary regardless of how you're building/organizing/deploying/operating the code.

> scales non-linearly

Indeed, https://en.wikipedia.org/wiki/The_Nature_of_the_Firm

Microservices are not the only way to split a system.

Far from it. They are the most onerous, least tractable way to get what you are going for.