Because it doesn't mean "not." It's a negative modifier, true... It's "a Latin prefix meaning "apart," "asunder," "away," "utterly," or having a privative, negative, or reversing force[...]" (dictionary.com unabridged) In some cases, it simply intensifies a negative effect. "-rupt" comes from a latin word meaning to break apart. In the case of "disrupt," the prefixes merely adds to an existing negative effect. There are numerous cases in latinate languages where a double negative is merely intensely negative rather than a reversal of the negative.
not allowed to come means you were dis-included allowed to not come means you were given permission to not attend
The prefix "dis" means both stop or end such as in discontinue. It also means "mal or bad or negative or not" such as dissatisfied, dissonance or discordance.
'Dis fromage' means 'say cheese' in French.
Dis means away
DIS means disqualified.
The prefix of disinclination is "dis-", which means "not" or "lack of".
The prefix 'dis' means not or the opposite of something.
No, "dis-" is not a prefix in the word "discernible." The prefix in "discernible" is "dis-" which means "apart" or "away."
The stem "dis-" means "apart" or "away" in words like disassemble (take apart), disconnect (separate), and disappear (vanish).
The word with the prefix "dis" that means in the state of not believing is "disbelief."
DIS means Daytona International Speedway.
The prefix of the word 'disappearing' is dis.