> If you have a good architecture and keep good code hygiene

That's a big "if" however - customers have a tendency to come up with requirements that aren't covered (or only covered in awkward ways) by the architecture you envisioned initially, while many of the well-architected parts will remain unused.

Then redesign the architecture. No need to go for a full rewrite as it can be done progressively. One thing I’ve seen is that people can be afraid to delete code, even if it’s not used anywhere.