So I read this (yes, it's in Hungarian):
https://index.hu/gazdasag/2020/03/09/a_szaudi_domping_es_a_koronavirus_miatt_osszeomlott_az_olajpiac/
... and now I'm smart.
Basically, in the past years the demand grew steadily, and the supply was forced to level it artificially, and so they kept the price up. The high oil prices ofc is good for every oil producing country, but some - where the cost of extraction is high - can't do without it.
This year due to the corona, the consumption fell, then on Friday the Saudis and the Russians said fuck the agreement which held back production which gonna result in higher supply. Then came the Italian crisis with the quarantine of the north, and the general mood in the EU (the fear of disease) suggests the consumption will even less than predicted so the scissor of supply and demand opened wider, resulting the fall of oil prices.
The low price of oil hurts all the countries who produce it, but not equally. The Saudis cover most of their budget from the oil, but they extract it the cheapest, so on the long run, when others fell out from the game their market share will rise. Russia relies less on it then the Saudis and still produces it cheap so they also win on the long run. But the US companies for whom the cost is high will lose badly this can be uncomfortable for Trump during the election.
For Hungary the low prices are favorable, since we are consumers, and it will help our import-export balance.