It's because the Go philosophy is "tests are code", so you use the standard language features like != instead of a whole new domain-specific language that you have to learn. I've written more about that here: https://lwn.net/Articles/821358/

Personally I find the "cutesy" names like Expect(a).To.Equal(b) and It("should ...") patronizing and too English-like (code is not a human language). Similarly, I wouldn't like a language that made you write:

   Please.Print(1.Plus.2)
   Log.To(Console).Text("did something")

The vanilla Go approach can get a bit verbose when you're doing lots of asserts. In that case, you can use standard language features like refactoring things to variables or helper functions, or table-driven tests.

But if you really want assert-style code, I like the https://labix.org/gocheck approach:

   c.Assert(a, Equals, b)

Because there's only one function (Assert) and a bunch of comparator names to learn.