Reaching Out and Back
The simplicity of this start may hold the key to why it is the most common approach. All that is involved is heading away from the line on a port reach a few minutes before the start and then when half the time remains tacking onto a starboard reach to head back towards the line. As the line is approached you come onto the wind to set off on your starboard tack.
This approach is straightforward and if sailed well allows you to cross at the right time by luffing up to slow down and dropping off to speed up.
It is common for much of the fleet to clump together because they are all sailing this approach. This makes this approach a poor strategic choice. The savvy skipper will minimise this by creating as much room on either side of his boat as possible by heading up and down. This results in the boats below you sailing much further down the line at speed.