Its a similar itch as programming for fun, but often that becomes less fun after spending the entire day programming for money. Factorio is just different enough to still be fun and relaxing, even though its similar.
Programming also comes with baggage that Factorio can do away with (eg sibling comment mentioned build tools, I've given up on an evening of personal programming before because setting up the build environment was too much effort... looking at you cmake you piece of garbage... Or because I hit a bug that was too much effort to find/fix. Factorio "debugging" is much simpler, its about finding blockages or optimizing things, not figuring out why undefined is not a number in some deeply nested code where the value couldn't possibly be undefined but it turns out some async code changed it without you realizing...)
Programming also comes with baggage that Factorio can do away with (eg sibling comment mentioned build tools, I've given up on an evening of personal programming before because setting up the build environment was too much effort... looking at you cmake you piece of garbage... Or because I hit a bug that was too much effort to find/fix. Factorio "debugging" is much simpler, its about finding blockages or optimizing things, not figuring out why undefined is not a number in some deeply nested code where the value couldn't possibly be undefined but it turns out some async code changed it without you realizing...)