Because they are a moderation feature of the forum software.
Every time anyone is issued a warning, their warning point goes up one (or more). However, the only people that can see the points are the mods and the actual member - this isn't a public number.
There are additional features I could activate relating to the warning points, but for a number of reasons haven't.
For example, i've been wanting to activate the warning point expiry feature - which would allow those points to expire after a certain period of time.
We can also activate a feature that would automatically suspend anyone that hit a specific warning level - however, I don't like that feature very much, so I decided to leave it off.