Not engineer driven orgs _and_ their product people don’t know how to drive the product or set requirements, or engineer driven by the type of engineers who love to tinker without making any real progress business wise

These CRUD apps need complex business rules, requiring expertise in the domain and making them configurable on the application level for customer while trying to keep the app not bloated.

Scaling is not the only challenge engineers face, but somehow it's the one that is mostly praised.

They also need to respond to customer requirements, which IG never needed to do while they had no actual customers. And as soon as fun was up and IG had actual customers (spoiler alert, advertisers) what a surprise 3 devs was not enough.

They also need to quickly respond to downtime, because unlike IG if some of those CRUD apps go down in B2B world you are often losing customers actual money not just ad views

Ad views translate to actual money??

Sure. If you are full on marketer you can say "not see an ad for service" is as bad as "service does not work".

But anyway there was never a period where Instagram had a tiny 3 dev team and handled ads at the same time. 3 devs only worked back when there were no customers, no ads, no profits and no real responsibilities.

They stayed true to a single product purpose, did not add frivolous features and experiments, and didn't deal with payments/billing, eventually being "rescued" by VC money? You seem to gloss over that AWS also helps them out a lot already here, by being the load balancer entry points and ordering VMs from a api.

There's no glossing, I just don't understand. It's also far from my corner of technology.

Still, between 3 devs and thousands, that's 3 orders of magnitude. Let's take the core team and 30x them for a broader project. Add 50 (?) for billing. Another 50 for web apps. Another 30 for general devops? That takes us to a "mere" 220 devs.

Then I read that Uber had around 2,000 SEs in 2020, and Airbnb at some point was 1,200. I don't know how to grok that.

You mention AWS, my impression was that even many very large orgs run their their hardware in the cloud (surely not all but still).

There seems to be a pretty big difference in business logic and requirements between a photo sharing app and one that moves or houses people.

Dealing with payments globally to hosts/drivers and specifically compliance is complex in itself.