Honestly, they grinded.
French Montana, as average as he is as a rapper, worked very hard to make his connections. He was hitting the streets interviewing people, talking to people, selling his dvds. Pure hustle. That's why while I don't like all his music, I respect him.
Khaled did the same thing, he worked hard in Miami to make connections when everyone flocked down there for a bit. He went from Fat Joe and Akon to getting paid by Snapchat...you have to salute his annoying ass for his hard work.