That's the problem with people, which I have noticed in my circle, they want to spend time self-learning skills but that skill doesn't guarantee income. Self-learning interviewing can increase your income significantly and people don't quantify it that way. Just a simple phone interview can instill confidence in your own abilities and increase your pay, or reduce stress by being able to figure out if a company will be a good/bad fit for you. If you interview enough you can figure out little nuances such as a micromanaging manager, a team that works late on Friday's and so on from a 5-minute conversation.