This is not a universal truth. I’ve worked with COTS products that required a ton of work to customize and get working properly - sometimes costing as much in time and manpower as it would have been to build the same
thing from scratch. Often this happens with managed server all-in-one “business solutions” systems that let non-developers build UIs and reports (and charts/visualizations,
etc.). Nearly 100% of the time this is inadequate and often completely fails, requiring management to bring in actual software engineers to “fix” things and eventually just rebuild an entire dashboard from scratch using real development tools and techniques. Many of these kinds of shops underestimate the importance of strong software engineering practices and fail to understand the complexity of their own requirements, much less the complexity of their data.