Why should an average programmer learn automata theory? Good programming relies heavily on choosing an efficient algorithm for the task at hand and yet an average programmer hardly uses 50 pages worth of algorithms from the Cormen book in his/her career.

Recently I started reading some CS books, long after completing my bachelors degree. One of the books is the Theory of Computation by Micheal Sipser. Although I love the content and still am in the beginning chapters, I cannot imagine where I would use the information provided in this book in my job.

What is the use of Automata Theory in the industry?
Automata theory is rarely used by practicing programmers today.  It is in principle useful for building compilers and parsers (though most developers don't need to do that today, and often use tools to help them).  Some of the concepts can be useful for building state-machine based systems, which are widespread (including, e.g., embedded systems), though it's not clear you need to know all the ideas from automata theory to be successful at that.  Also, many people study theory even if there is not a direct practical application.