Didn't you start a thread with exactly the same question about a year ago? If not you, it was someone with a similar forum style.
Bike racing has been around for about 120 years, ample time to determine that 100 yards is not enough distance for bikes to get up to full speed. You might as well ask why there aren't 10-foot-dash running or swimming races.
Here are a couple of examples from videos chosen at random.
Closest equivalent, solo:
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Closest equivalent, head to head:
Track racing looks good in videos. If you're really interested and not just posting out of boredom, look up some races under, e.g., World Championship sprint, World Championship miss-and-out, World Championship kilometer, World Championship points race, World Championship keirin, etc.