Larger animals can be inspected individually to find pathogens or diseases.
Insects are so small that it's practically impossible to inspect each individual organism. You can do sampling of the batch, but the odds of missing bad ones are still high.
Same with the fruits and vegetables, some are easy to inspect, others are almost impossible, or impossible to clean. There are kosher (insect-free) versions of lettuce and some berries which are much more expensive than non-kosher ones.
Lastly, disgust is a part of the human immune system. Religious dietary laws and cultural taboos are probably partly developed from disgust, and partly from trial-and-error.
Insects are so small that it's practically impossible to inspect each individual organism. You can do sampling of the batch, but the odds of missing bad ones are still high.
Same with the fruits and vegetables, some are easy to inspect, others are almost impossible, or impossible to clean. There are kosher (insect-free) versions of lettuce and some berries which are much more expensive than non-kosher ones.
Lastly, disgust is a part of the human immune system. Religious dietary laws and cultural taboos are probably partly developed from disgust, and partly from trial-and-error.