Leaving a job soon for better pay. What’s a good reply for when the current employer says “Why didn’t you ask for more?”

Little background. I've been working for the current company for 3.5 years for a relatively low wage and they hired another guy a few months ago paying him an extra 400€ above my salary. I've never been the type of person that asks for more money. Either the company sees worth in your work or they dont. If they do then they will naturally raise your salary. I'm thinking about what to reply in the event that they ask me “Why didn't you ask for more money?”. Thanks in advance.