It is because an exploit (and a feat) can be either good or bad, it just means something someone has done. "exploit" can also mean like "adventure": His exploits in Italy were well known.

You seem to have misunderstood the meaning of 'exploit'. There is nothing at all in the definition of the word to suggest that these are positive achievements. Exploits are daring, dangerous or exciting things which someone has managed to do. In fact, they are more often negative, or at least controversial. One other important point about this word : The pronunciation is not the same as the verb. Whereas the verb stresses the second syllable, it is essential to put the stress on the first syllable of the noun - the noun is pronounced "EXploit'.

Exploits aren't always positive. The term is used also to describe a means to take advantage of a security vulnerability in computers. merlyn's answer is good.

Exploit, when used as a noun does not necessarily mean such things are positive. These days, dictionaries are not consistent in defining the meanings of words so you have to be careful just what dictionary you use. Just spend some time comparing how they each define certain words and you are going to see disagreement on some words. This is because dictionaries compete with each other and there is no real authority guiding the meaning of words. Meaning changes with time and current usage in all languages. After a particular usage becomes common it is often accepted by and included in dictionaries. Some dictionaries are more liberal than others in determining when a definition should be updated. The problem is that if they change too often and are not consistent with other definitions it can really be disruptive to what is established meaning in a language. This is why I tend to be conservative about the definitions of words and rely on the more conservative Oxford dictionaries to determine the correct meaning and use of a word. I think this is also the best practice for language learners.