system
Given the following post, respond as if you're commenting on Reddit:
human
[LOTR & The Hobbit] A question on trolls

I have noticed in the events of There and Back Again.(A Hobbits Tale) by Bilbo Bagins and The Lord of the Rings by Frodo Bagins that the sentience of trolls changes dramatically in the roughly 60 years between the two events. By this I mean in Bilbo's story they are capable of conversation and reasoning, where as in Frodo's Story they are unintelligible brutish creatures with the only concept of I'm going to wreck the shit out of that thing in front of me. Is there an explanation for the seeming loss of sentience?
gpt
the trolls bilbo met were natural trolls not Olog-hai. 

The Olog-hai were a breed of troll created by sauron for war, they can survive sunlight, are larger and far more powerful than ordinary trolls - it seems likely he would have bred for brutish traits and compliance.  It is these that marched out of mordor to war and as such these that the fellowship met on their journeys.

edit: it's worth pointing out that bilbo was known to enhance stories a little for dramatic reasons - his trolls are rather more intelligent than the average, most are more like the rediculous cave-man stereotype in modern films.