As I understand it, as you kill the bosss in sequence it sets a series of flags that can enable and even disable certain types of raids, another factor I believe is the environment where you are when the game rolls for a raid event to occur; I.E. the way I've set my primary base up, usually when I get a raid, it's almost always "the ground is shaking" which is lamentable but also fun, because while I rather enjoy fighting mega mobs, the trolls get a little tiring after a while, particularly since they tend to have the greatest potential for wrecking your entire base within a very short time if you fail to keep them occupied.

Skipping the bonemass has a fun consequence of preventing a whole bunch of extra raid events from being enabled, like potentially being attacked by a raid of wolves at any point in the mountains or plains, even without a raidable base nearby.