Off-the-shelf software is built for everyone. That's the problem.
When software is designed for a wide audience, it can only go so far for any specific business. You end up adapting your process to fit the tool, paying for features you never use, and building manual workarounds around the gaps. Over time, those workarounds cost more than the software itself.
Bespoke software is built the other way round. The process, the users, the data — all of it shapes what gets built. The upfront cost is higher. But the long-term fit is completely different.