'Cos the Japanese had already been competing sideways way before Formula Drift came up the idea.
Drifting is a stylish form for moving forward. It goes hand-in-hand with eargasmic engine sound which gives you goosebumps, and tasteful, fragnant, thick tyre-smoke. And brings much fun. If you might want something to "blame" for that (in a good way), do it with Japan's geography in the first place. Approximately 3/4 part of the country is highlands and mountains, hence there are much steep, narrow, curvy roads separated from the abyss with a plain metal barrier. It was only a matter of time for the local to push the art of countersteering and turning with the right pedal to the limits.
The first amateur drifting contests were held just for fun and self-entertaining, but they made their way by time: the preparations for a professional, competitive environment started in 1999. Later the madness started spreading outside Japan. The rest - as they say - is history.