That may be because the minimum wages are massively different for the two countries, with $0.48/hr in Mexico vs $4.98/hr in Spain[1]. Globalism does exploit the lower standard of living of other countries, after all. That means that even though there are massive tariffs, these "third world" countries can still make a profit because of the abysmal quality of life for its citizens.
Of course it's because of wages! The point is, it is because of protectionism that Mexican and African farmers cant sell their products in to the EU at a fair price, and once outside the customs union, the poorest consumers in the UK and the poorest farmers in the world both stand to benefit. Global trade is lifting billions of the poorest people out of poverty, and long may it continue.
It's true that globalization is raising the average income of people in many places in the world, but it is also causing an increase in inequality within most countries[1]. It's not fair to the middle class of a country when it needs to compete against a country that doesn't have the same environmental or labor laws that it has. This leads to a race to the bottom and tanks the quality of life for most people, though the capital owners get out ahead. Why can't those countries form their own industries?
Serious question: What keeps Mexico and other smaller countries from forming their own industries and get their own economy going? Because if it's a systemic or governmental issue keeping their economy down, then why would we want to support that inefficient thing keeping it all down?
[1] https://en.wikipedia.org/wiki/List_of_minimum_wages_by_count...