Play games
Choose the game that interests you and play itfor free.
Complete the quests
Every game has some quests for which you will receive Soul Gems.
Receive rewards
You can exchange your Soul Gems for Steam Wallet top-ups, game keys, CS:GO Skins and other rewards.
Well if you get free robux it would not as fair as it is bought by money and people who have bought it for money would think it is unfair so thats why there are sites that scam people and take thier robux and data so they could harm them.