Many chefs complain about our habit of drinking cocktails before sitting down to a meal. Most people find a few rounds of cocktails can get things off to a rolling start, but you can see their point: they want us paying attention to the tastes of their food, instead of just focussing on not sliding under the table.
Apéritifs are drinks designed to keep you entertained or to allow people to socialize away from the table while the meal is being prepared. They are at least slightly bitter, as they are meant to stimulate the taste buds, not satisfy the appetite, the way sweet things could (which is why dessert is served at the end.)
They also have a low alcohol content, as they are supposed to make you eager to get to the table, not jump up and do the mariachi on it.
It was actually Italians in Turin and Milan who pioneered apéritifs, though French manufacturers soon caught on to the idea in a big way — witness the fact that we use the French word, apéritifs, instead of the Italian, aperitivi. Italian vermouths were among the first apéritifs.
The French word “apéritifs” comes via Old French from the Latin word “aperire”, meaning “to open” or start something, just as April, also from the same root, is the start of spring. (Some food writers have tried to invent a Latin word “apertitiuvum” as the source: nice try.)