Earlier quoted context omitted.
The business perspective shouldn't overlook the direct and indirect costs of engineer turnover.
Aren't these vagabond workers destined to leave anyway? They seem to me that they have this wanderlust to switch jobs and try something new every couple year and get a kick out of it. I don't think that there's much to do to retain them and make them feel excited all the time.
Even if not, they may not be paying attention to things that matter to your business, and may ultimately do more harm by staying.