The language was designed to be as simple as possible, as to not confuse the developers at Google. I know this sounds like something I made up in bad faith, but it's really not.

The key point here is our programmers are Googlers, they’re not researchers. They’re typically, fairly young, fresh out of school, probably learned Java, maybe learned C or C++, probably learned Python. They’re not capable of understanding a brilliant language but we want to use them to build good software. So, the language that we give them has to be easy for them to understand and easy to adopt. – Rob Pike

"It must be familiar, roughly C-like. Programmers working at Google are early in their careers and are most familiar with procedural languages, particularly from the C family. The need to get programmers productive quickly in a new language means that the language cannot be too radical. – Rob Pike

The infamous if err != nil blocks are a consequence of building the language around tuples (as opposed to, say, sum types like in Rust) and treating errors as values like in C. Rob Pike attempts to explain why it's not a big deal here.