For one, some engineers are grown adults with families and full lives outside of work, and they choose not to spend their free time coding. Some of the best engineers I've worked with fit in this category.
Secondly, I'm sorry, but it sounds like perhaps your work happens to not be very interesting or challenging. That is not the situation for everyone. I solve interesting, challenging, diverse problems all the time at work, on proprietary codebases that cannot be shared.