Well, I think it is the great feeling of accomplishment/achievements when you implement something cool.

Freedom, and the joy of creation.

I don't mean freedom as in "you can work whenever and wherever you want". It may or may not apply to you. Also, there are project deadlines you must meet, so at least "whenever" is not an option. Languages and frameworks are also not always your choice, especially if you work for a big company. I talk about implementation freedom. What algorithms, code constructs, and in general, solutions you use is always up to your creativity. And with that we arrive to the more important thing.

All artists enjoy when they finish their next masterpiece. I usually say code can't be finished. Still, when you finish a new feature, it's always joyful. You have created something other people will use with nothing more than your mind (and a bunch of keystrokes, but that's usually the smallest part.) A lot of people argue if software development is art or not, but when I see a well designed UI that works smoothly and does exactly what I need, I have no doubt a beautiful mind is behind it.

Keep up the arc of coding!

Working anywhere/anytime. It's why I started learning all of this.

Also, you are one of shockingly few people who have insight into the workings of the machines that virtually run everyones lifes.