Because nationalism was the only political force that could compete with socialism, so capitalists with the help of their Western friends went all in on nationalist propaganda. Ukraine also had the worst recovery from the economic catastrophe of the 90s, so its population was the most dissatisfied with the liberalism. Communists and anarchists there really failed to capitalize on it, so the fascists won and increased the amount of fascist propaganda tenfold. Still, Ukrainians mostly voted against Nazis, protested against Nazi takeover and literally launched an armed uprising in the East, so calling all Ukrainians Nazis is a big overstatement.
I'm most worried about young generation that was raised in situation of total fascist dominance in media and education.