You don't get to the big leagues by just applying to places. You earn the stripes. You put in the hours. You shed your blood, sweat, tears, and often a small fortune just to get in the door. And even then, you're scouted, you're courted, you're wined, dined, and then, if they like you, they'll ask which sponsors you're bringing to the table. At least, that's the normal route for MotoGP and other top-tier racers.
It's a business and marketing decision, and one that's largely made without a job application or cover letter—why won't those freakin' die already?—and made in a boardroom, not by some lowly HR person passing anything along to management. It's decided during silly season, as most race fans will attest.