also the fëanorians probably used quenya to be spiteful because of thingol's ban of the language.... which also would have a lasting effect on it's use, probably, in later ages- most of the noldor are dead or sailed once eregion falls and the last alliance is fought, & even those noldor had spent hundreds if not thousands of years living among sindar, so the use of quenya was likely limited among them! tbh logically, quenya was probably all but a dead language by the time the third age rolls around!
(also, I'm sure many of the sindar held on their the stigma against it even after Doriath fell, which would only help it fall into disuse)
Objectively speaking if I had my whole language banned I’m pretty sure I would do that too. Granted I would also try learning the other language just so that communication would be possible.
Personally I think that the ban sparked a lot of aggression from the Noldor just because so much of their culture was outlawed, the songs and their language even just their words. Ironic since the writing system was incorporated into the Sindarin language and culture. As a result there was a lot of prejudice from both sides directed at the other between the Noldor, specifically the Feanorians, and the Eldar in Doriath.
I agree though that the lack of Noldor around probably was a direct cause of Quenya’s disuse. I seem to recall somewhere it being said that the written form was still used somewhat regularly, unfortunately I don’t remember where it is mentioned.