Circumstance, though I can't claim to have any real knowledge on the ground. Any time the debate was brought up, I saw a lot of Leave people marginalized as uneducated racist xenophobes. It was that bullying tactic that ultimately backfired (IMO), not that Remain somehow appealed to the intellect.You think Remain had the most vical support? What are you basing that on. Many people seem to think Remain's fatal flaw was sitting on their hands while Leave was getting their message out.
Put it this way - I would estimate the opinions I saw in the media were 3:1 in favor of Remain. Remain made this an economic issue but failed to gain ground on that argument alone. It wasn't for lack of trying, it's just that they thought they were intellectually superior to anyone who'd have the audacity to disagree with them and didn't treat the people they marginalized and silenced as serious threats, but it wasn't for lack of voice. If you want to say my opinion is anecdotal, that's fine, but it's how I saw things as I became more interested in the issue. I wrongly predicted that Remain would win, so I'm not trumping my own horn.