Objective-C was designed by adding objects to C. So the base syntax is C. Then the idea was that the object-oriented bits were inside [], and the named arguments or message syntax came from smalltalk and was designed to make the language easer to read. Named arguments are very verbose, but they make the code much more readable.

Then much later Apple added the . syntax, which while more familiar to a lot of modern developers kind of broke the cleanliness that the syntax used to have.