“If people were insects, there would be more approved drugs on the market.”
It has been estimated that there could be up to 10,000,000 different species of insects which are divided up into about 32 orders.
The lifespan of insects range from a couple of minutes up to almost 15 years for the female ant. (the male ant on the other hand only lives a couple of days and then dies once he gets laid, lucky guy doesn't have to cuddle afterward)
Getting back to your question, today's drugs are only approved for normally two groups, whereas you couldn't have a one size fits all scenario covering the insect population.