My experience of loyalty is that often the important parts of it are in the differences people have. We all cluster around group norms, some group norms different than others - but they're large targets and any reasonably well run company will hit them. It's something they can get elsewhere, and so provides little incentive to stay.
Consequently people don't seem to quit companies, as long as the company isn't falling apart of course, as much as they quit bosses that don't take care of them. That are negligent - either through incompetence or absence - or abusive with respect to their needs.
If someone's leaving the company, it's often worthwhile to try and find out why - preferably talk to them a long time before they leave the company, so it never gets to that point. Try to find out what's going on in their lives, what their problems are, what they want to do, what they enjoy. Try to make sure you can offer that to them.
Some people want to feel like they're changing the world - that's your story group. Others want to learn to be better programmers. Others want a boss who can be flexible around their lives. Some people want to teach others. Some people just want days off for their kid's plays. Whatever their needs, most people seem to want to feel like they're important; like their opinions and their problems matter to you. Like they're not just another cog in the machine.
Things built on that sort of platform are a form of personal loyalty, that they can't easily get at other companies. They go to another company, they may talk to them about a mission, they'll probably be growing, they'll want to have a good team (whether they do or not's debatable - again, see people don't quit companies as much as managers...). But they won't have that relationship you've built. And their future bosses might be awful, it's a gamble for them - and it's not clear their winnings will be significant, at least provided you're not stiffing them on pay or something like that.