Though I agree with you, I'd argue that namespaces took so long due to the fact that (as you state in your post) PHP is the most widely used scripting language

Though I agree with you, I'd argue that namespaces took so long due to the fact that (as you state in your post) PHP is the most widely used scripting language today. Like all widely used languages it evolves more slowly than those with smaller or niche communities. The PHP devs focus has clearly been stability and integrating the most widely used extensions into the core. As you yourself said, "so goes the life of a language whose design is driven by demand and not theory."