Eh, there is a really sharp line between the various things that are more loosely called modeling, or in various ways resemble modeling, or indeed doing some of the same things that models do on the one hand, and being a "model model" on the other--that is, being professionally signed to the fashion or commercial divisions of a handful of elite management companies. For those you have to have a very narrow range of height (much narrower than normally described), one of a specific (and to some extent varying from year to year) type of looks; and it's quite common to be "discovered," but almost always by agency employees who happen to run into you; if it's by another legitimate party, a top-level photographer, say, you'll be sent straight to an agency after the shoot to continue your career. I'm simplifying a bit but this is the essence.

Mere "good looking dudes" should not get their hopes up as to whether they could ever be a "model." In truth, they cannot. It doesn't mean their own type of handsomeness isn't just as good, or even superior, to those of real models. If Zac Efron, Joe Manganiello, or that kid from Weeds who supposedly was a model on the show had ever showed up to a real modelling agency instead of becoming actors, they would be lucky if the desk clerk made any effort to stifle her laughter.