Valve hates 3

Valve has made many popular games in the past. They made the left for dead series and team fortress 2. But they never make a third game. They have 2 team fortresses. 2 left 4 deads. 2 portals. And in half-life, instead of making half-life three. They made half life 2 episode 1. Then they took it to half-life 2 episode 2. But still no three.