From the first appearance there were so many rejection, some people blamed BCH for the decreasing of bitcoin price and you can see how people reacted after BCH is out, people directly sold their coin for bitcoin, so actually from the first BCH already lack of interest
Exactly, that's what I think happened. We can see way back that bitcoin price increased drastically a week before (and even after) the August 1 forking. People might have switched to investing in BTC, put their money on it before that BCH forking, and took the opportunity to get the free BCH equivalence of their BTC. In my opinion, they are after the earning from BCH, and didn't intend to support BCH afterall. And again, in the coming October 25 forking (the creation of Bitcoin Gold), expect that the price of BTC will rise up again. At this moment, its value is surprisingly increasing. And expect it to fall again some weeks after that forking.