"10 years" . In mls? Especially if he's good? Excluding Gk's it just doesnt happen. You can name a few exceptions like dolo,maldini, giggs etc. but they're like .00004 percent exceptions....and thats europe with cap and bullshit mls limitaions.
You are missing the point. It's not whether they will stay ten years, but that you find players who can contribute for a long time. It allows you to build an identity that doesn't need to be constantly retooled and it makes it easier to manage the roster process.