User blog comment:Kogath/Monster Hunter 4 Ultimate for the Nintendo 3DS/@comment-17735225-20150326150004/@comment-17735225-20150327170053

Knowing who the real 'don' is might change your view about what the egg mafia can do ;) I suggest you find out who he is. It might lead to a lot darker unspoken lore about Dundorma and wyverians.

Other explanation from that dialogue is that one/some of the fatalis eggs they secretly kept hatched and have to be killed, and since fatalis is supernatural it can sense that, prompting an attack.