We don’t know why those 3 hybrids have been removed from the sequel, as of yet, Frontier haven’t explained why they have done this.
In my opinion, it doesn’t matter whether we liked them or not, their removal from the sequel is deeply unfair and rather detrimental.
It’s deeply unfair because every single dinosaur from the previous game has returned for the sequel, including species that had mixed to negative reception from players and the two species from the same DLC as the hybrids. Yet for some reason, the hybrids are excluded.
It's detrimental because with the removal of the two herbivore hybrids and only piscivore hybrid, the sequel has lost variety amongst the hybrids. As much as I love the Indominus rex and Indoraptor, they are both carnivorous raptor hybrids and the latter can be easily argued as just a variation of the former.
Therefore I'm strongly advocating for the inclusion of Ankylodocus, Spinoraptor and Stegoceratops, preferably via a free update.