There are various reasons cited. Again, there's the decision not to import. Another is hoarding and price manipulation. There's also the fact that it's holiday season, although the price has already been rising for months. As a matter of fact, just 6 months ago, a kilo is only around $2. But of all the reasons cited, none is convincing enough.
This of course shouldn't be the reason but it would be for sure the cure!
We have experienced the same price scare with sunflower oil in Europe, hoarding, people panicking and importers asking for huge prices but, immediately in a free economy the laws of offer and demand started kinking in, and rapeseed oil started to enter markets that used only sunflower, imports started to look very profitable form other countries, as soon as the profits from doing so looked juicy then hundred of tons hit the market, from 5 euros per liter it went down to 2-3, slightly above the prepandemic prices.
Now look at the differences here, even assuming I would fill a 10ton truck from a chainstore so no producer prices, I would pay 15k euros, I would spend 5000 euros on gasoline driving from Paris to Manila, rent a boat for another 5k, all the time stay in 5stars hotels, so that's about 30k euros but I could sell my cargo even at half of the price 6e/kg for 60 000euros, so that would be a net gain of 30k euros using the most ridiculous and expensive way of shipping goods!
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I'm not sure the UK and France are good comparisons for onion prices as I'd assume they'd remain pretty stable since wild garlic is abundant in the UK (to an extent apparently a lot of people didn't eat it before the 80s because it was considered a weed).
I quoted US walmart prices, too, the max is 4$ for the best batch in
Woolworths Australia, and ~3$ in
stores in Brasil when the whole world has 1/4 or 1/6 of the price something is wrong there.
I've checked some random prices in superstores in the Philippines, and there is no such difference on anything else.
This is not something triggered by inflation, this is something local done by stupid politics.