They do that to make the list long enough that you tune it out. They have to list the downsides , and are only able to mention benefits that have been proven to help with approved uses.
They don't have to communicate the actual likelihood of the risks or benefits, or communicate the risks in a way that conveys their gravity.

So they can leave out the part where most insomnia medication only gets you 15 more minutes of sleep, and lump the 75% chance it'll leave you so groggy the next day you can't drive a car in with "if you're allergic to it, taking it is bad".
Because you were warned. "Most people will experience improved sleep duration. May cause lingering fatigue. Do not take if you are allergic to it".