Though there were no plans in the books for a third installment of Castle Rock, fans had hoped that Hulu would come through on a Season 3 after the first two seasons' success.
Apparently, Hulu's known that the series wouldn't be continuing for some time. While Warner Bros. TV used to be a primary source for Hulu's original content, the brand has since shifted its focus to HBO Max (which makes sense, since they're under the same umbrella). Don't hold your breath on a Castle Rock shift to HBO Max, either.
The first season of the Stephen King-based series focused on the infamous Shawshank Prison, with the ever-creepy Bill Skarsgård acting as the seasons' strange but seemingly soft protagonist. Meanwhile, Season 2 followed Annie Wilkes (Lizzy Caplan) in a Misery-based storyline that was both heartfelt, odd, and admittedly sometimes a little slow. Skarsgård's character acted as an easy throughline between the seasons.
It's a pity we wont be seeing more of the J.J Abrams produced series. Abrams, for all of his film-sins, really thrives in long form (television) focused narratives. All of the performances really shone, and the series offered an exciting spin on familiar King storylines. Though it's always the hope that someone will swoop in and save a series in circumstances like these, the Warner Bros. TV situation makes it pretty unlikely that we'll ever be getting more of Castle Rock.
