Italy has convinced the world that it is the king of liquid gold – hiding the fact that a significant proportion of "Made in Italy" olive oil comes from Spain.
Italy has a fraction of the territory of Spain, of which a fraction is usable in agriculture (Italy is mostly mountains), and a fraction of that can be used for Olive trees. Of course Spain has more yield, with their immense spaces and flat fields.
As for selling more or less, it's just a supply chain thing, Italian companies were better placed to sell it, but the bottle clearly states when it's Italian oil and when it's not.
These sort of antagonizing takes intra-EU are not helpful.
Italy is 60% of the size of Spain and has a similar ratio of arable land (27.1 vs 27.9% per Wikipedia, Spain is also quite mountainous). Doesn't really invalidate the point in your comment, but I expected a bigger difference when comparing "immense spaces and flat fields"to a mostly mountainous fraction of the territory