"Everything should be built top down, except for the first time", as the saying goes %) The problem is often that new things are built with tools that allow for flexibility, because the builder hasn't decided on the shape of what needs to be built. In 1990s it was Perl, in 2020s it's vibe-coding, but in either case it's lax and "dwim".

As the developer attains a much better understanding of the product, strictness becomes more and more beneficial, but the spectre of backwards compatibility haunts the interfaces and defaults.