Yes, exactly, it’s about controlling the dosing. If you haven’t eaten for a while, or only had fluids, and then suddenly eat medicine, it’s more likely to be vomited out, so nobody knows how much you had.
If you can’t keep food in, medicine won’t work that way either.
Eating pills on an empty stomach can easily cause acid reflux. Since about a fourth if all people have acid reflux issues, it’s probably a good idea to advise people to down pills alongside other food that’ll stay down.