While using the GLM c++ library, why do I need a scoping operator for vec3 but not dot?

Question

While working on a recent project I noticed that I did not need to scope the dot product function but I do need to scope vec3 for example. Why is the library setup like this?

// compiles
dot(vec1,vec2);

// unknown type error, 'did you mean glm::vec3?'
vec3(1,1,1);