The sandwich fallacy comment nails it. The hard part isn't the building - it's the understanding.

When you're at a particular layer of the stack, you understand your immediate customer (the layer above you) reasonably well. But two layers up? Three? You're basically guessing. And the higher you go, the more the problems become messy human problems rather than clean technical ones.

I build accounting tools. The technical work is manageable - parsing bank statements, matching transactions, posting to ledgers. But understanding why a bookkeeper categorises something a particular way, or what makes a reconciliation workflow feel "right" vs frustrating - that took years of sitting with actual users and watching them work. A database company could technically build what I build in a few months. They'd never ship something anyone actually wanted to use.