They said that’s how it works in the dev blog introducing map voting. If you didn’t get penalized then that’s a bug.
Map Voting: Choose the Map, Shape the Match
Map Voting goes live at launch in Quick Play and Competitive, letting you shape the match before it starts and control where the action unfolds. After role queue locks, you’ll get three randomized map options to choose from. Every vote adds a 1-in-10 chance to that map’s odds, and the winner is selected using a roulette style roll.To keep things chill, team chat, battle tags, and individual votes are hidden, so there’s no pressure—just a better chance at playing on maps you love. And leaver penalties kick in as soon as voting starts, so stick around and make it count.
Your match, your map, so take the fight where you want it.