A question about Ranked progression

Might seem like a daft question but, i’m just curious as to what actually causes your progress to go up in Ranked matches. Is it by winning matches, or is it down to how many kills you get?

Reason I ask is because I played some objective matches earlier and a few players blatently would not pick up the Oddball to help our team win the match, but would instead just focus on getting kills.

Your K/D and that’s it.