The honest answer is that I've outgrown the size of the problems available to me, and I'm moving toward bigger ones. My current company has been genuinely good to me — I've been promoted once, my manager invests in my development, and I'd recommend the place to a friend. But we're a stable forty-person business, and I've now automated or systematized most of what my role contains. The projects that would stretch me next simply don't exist at our scale.
This role has them: the posting describes exactly the multi-team coordination and process-building I've had small tastes of and wanted more.
I'm not running from anything — I gave my current job my best and it shows in how I'll leave, with everything documented and a smooth handoff. I'm running toward the version of this work I can't do where I am.