Yeah it is a strange choice, maybe just reflecting what the creators of Go are used to. They have always had null and haven't had any problems with it, why change?

Null made since in the early days of C, an option type back then would have been prohibitively expensive. Today, not so, any language that can afford garbage collection, the cost of an option type is lost in the noise, and modern compilers can often optimize the cost away entirely. (though that would hurt Go's fast compile times a little bit)