Modern architectures look like this: https://github.com/donnemartin/system-design-primer

All of the pieces have complex and emergent behaviors as they interact with each other. Many (most?) are hosted, not even fully in control of the team using them. Recreating this environment in a hermetic way for testing is either actually impossible, or so cost prohibitive as to be practically infeasible.

I'm not the person you're responding to, but having the same software and hardware is possible (most of the time), but production environment is a living thing. To simulate production you need the same data and interaction you have in production, and that's quite difficult to do in many systems, if only for regulatory reasons (PII, PCI and friends).