In all fairness, HN and SO are fairly straight forward CRUD apps (esp HN) with a limited amount of 3rd party integrations. On the other end, you have companies

In all fairness, HN and SO are fairly straight forward CRUD apps (esp HN) with a limited amount of 3rd party integrations. On the other end, you have companies like Zapier that integrate with 6k+ external services. With something like that in a monolith you'd be constantly redeploying to fix changes and you'd have a pretty wild dependency tree if you wanted to use official SDKs