So we will have a straight fight between Dobrev and Marki Zay. That strikes me as a huge difference in ideology. One would think Dobrev would be the clear favorite as Marki Zay's ideology is anti Orban conservative while Dobrev would be in the middle of the left leaning opposition, but perhaps many otherwise left leaning voters might be attracted to the idea of voting for someone who might have a better chance of defeating Orban and Fidesz.
For rather obvious reasons, Bulgarian coverage of the Hungarian elections has been focused on Dobrev (who, after all, is half-Bulgarian and was born in Sofia) and to a much lesser degree on Karácsony, with Márki-Zay dismissed as an also-ran and consigned to a sentence or two towards the end of the article. So I may be very wrong, but my impression is that ideology plays a very small part in this primary.
In my understanding, the main reason why Karácsony withdrew is to avoid a duel between Orban and Gyurcsány-by-proxy (fairly or unfairly, Dobrev is seen as an extension of her husband). The thinking is that if confronted with a choice between two crooks, the average Hungarian, however disgusted with Orban corruption and antics, will still choose the crook who brought about relative prosperity and stability than the one who pushed the country to economic ruin and chaos.