Valorant is a game about space and angle control. And imo, its usually more important to take and hold more space away from the enemy instead of giving it up for a safe plant. Unless you are omen with ult, it usually takes you longer for you to rotate to the other side of the map as an attacker than a defender unless you go through mid, so you actually give the defenders a chance a chance to make a come back. Even if you are omen with ult, your teammates aren't, so they'll be stuck at the other side of the map, vulnerable to potential lurks. If its already a 5v3, why not play those odds instead of making it a 2v3 then a 3v3?

This is actually the part that most people don't understand about defaults and playing for picks. It takes longer to capitalize and position on each pick since everyone is so spread out in comparison to rushes. And whatever number disadvantage the defense may have is mitigated by the time it takes for attack to rotate, giving defenders a chance to position better and potentially clutch. By taking space and contesting them, this option is much riskier for defense, and in lower to mid elos, players just crumble under the pressure. Not only does it limit the options of the defenders, but it gives you more options as well: you can fake rotate to get more defenders into their own spawn between two sites by making sound through running and utility. Just be sure to walk to not give them any info unnecessarily.