It's honestly just some kind of addiction.
First it starts with this eye opening realisation that not only are people different, but there seems to be a structure that explains the differences. You're given a lot to work with right off the bat, and it's not something trivial like... how to change a tyre. This is about understanding people. It has a huge amount of utility.
Then comes the phase where you run into inconsistencies, problems, things that don't add up. Naturally this makes you want to resolve these issues. Because after all, the goal is to have a complete understanding of people. If there's an inconsistency then that means you don't have a complete understanding. So it always feels like there's something more to learn, and something more to contribute.
Then comes the phase of meeting new people and talking about it. Getting their opinion, and just socialising in general. You start to feel like you're apart of something. You make friends, but you also make enemies.
Then comes pain. You meet people who aren't as far into the journey as you are, and you get tired of explaining the same thing over and over to new people. You start seeing fights, biases, stereotypes, type discrimination, and people complaining about such things.
So you try to let go and forget about it. But you've already spent so much time thinking about it. It's lead to some great experiences, so how can you forget about something that once seemed so important?
Thinking is honestly just an addiction sometimes, and MBTI and cognitive functions provide an infinite amount of food for thought.
What do you do with all the technical knowledge? Have you been able to apply it in real life?
For me the original purpose was to understand myself so I could plan out my career and life with the overall goal of being happier. But I found value in using functions to better understand where other people are coming from. It also helped with socialising - I'm not naturally someone who is interested in other people in the slightest. So having something to "do" while talking to someone (i.e analysing them with cognitive functions in mind) helped me talk to them without getting bored.