Web developers are amazing. When it comes to building website tools and functionality, they do things that I can barely fathom. But let’s be honest: Web developers are not SEO experts. Their job is getting code to work based on some specifications they are given, but they don’t often think about what is best for the site from a search engine perspective.
I always recommend getting an SEO involved when building or designing a new web site. They can often provide details that web developers simply wouldn’t consider. One of those details is the site URLs.