It’s possible it’s down to what you say about them too. Example: you tell them the bonus is $777 and they find out it’s $200 or something like that. Or they don’t like RTG and you don’t mention it’ an RTG casino. Or they deposit with credit cards and the casino doesn’t take them. Maybe they arrived at your site searching for “Thunderstruck” and they clicked out to find out if the casino had it. Could be any number of things.
I always think that you have to try and send a player to a casino with lower expectations than what the casino actually gives them. You might get less clicks, but you’ll get a higher % of signups. If you send them with higher expectations, you’ll get more clicks, but a lower % of signups.