Comparing store-bought chopped garlic
Olive oil isn't cheap enough to be an inexpensive filler, and the garlic has to be in something -- either another (cheaper) oil or vinegar.  Garlic and olive oil is a common combination.

The sort packed in vinegar also has its uses and keeps well. It's the only chopped option I can easily find without added salt.  But when the proportion of garlic in the dish is high the vinegar flavour isn't always desirable (so I use fresh then).