Making software work for single use is relatively simple, making software that runs at 100% uptime, with large numbers of "users"/"tasks"/etc is an entirely different level of development and design.

The actual functionality is a very small part of software development.

Making it work within its constraints (memory/CPU/network/storage in the small scale, ability to handle peaks while maintaining uptime at a larger scale), as well as dealing with the "non-functionals" like AuthN/AuthZ, obervability, performance, etc is actually the "hard part".

Then add in business "non-functionals" like "minimize CapEx/OpEx", "meet external SLAs with measurable and reportable KPIs", "meet corporate and regulatory standards and requirements" etc.

All of that is much larger than the actual function being developed.