In this case, their free time breeds free time (barring an employer issuing more work). The logic works in some situations.

I work in an automotive company (one of the big three's) I specialize in Noise and Vibrations. My job description involves testing, analyzing, and solving problems. Everyone I work with has very little to no programming experience (edit - programming is not a part of my job description). We* deal with huge amount of data (coming from sensors and microphones) I like to build custom tools (write software to process the data) so when I am really solving problems, I am spending very little time/effort in data processing and more on analyzing. (edit - a lot of people dont appreciate the things I do, they like to spend hours on running calculations using a standard software that we have, I see this as waste of time since it can be and should be automated)