the exploit is at the most basic level of operation, imagine if there was a problem with a car that it made so much horsepower it always spun on acceleration, so it quickly burned thru tires, but the tires it had were the best physically possible, well then the only fix for the problem would result in the car being slower. The basic level of operation is there to increase performance, any fix to filter for exploits would add instructions and complexity to everything the processor did involving this performance gain feature and thus would make its performance benefit less. Intel has added a feature that makes their processors have an edge but the feature is unsafe, imagine buying a guy with a special part that makes it shoot the bullet faster, more accurately and with more power, but it makes it more likely to blow up in your face, then imagine this gun costs significantly more money; that is probably a better analogy.