It is more than brand loyalty. Technologies (particularly programming languages) shape your thoughts and the way your mind structures solutions. This makes it particularly hard to admit when your pet technology is lacking; you are also disparaging yourself! It is tough (impossible?) to be detached in such technical discussions unless you are very familiar with neither or both of the alternatives being considered.
that's very true, a programming language you've mastered begins to influence the way you think and becomes part of your identity. A criticism of the language becomes a criticism of yourself which is very uncomfortable. The only other thing I can think of, off the top of my head, that gets ingrained the same way is politics.