The insistence that it wouldn't affect sovereignty was precisely why folk considered the stories that it would, were propagada, and disbelieved. And ultimately much of the reason we opted to remain in. One learns to be cynical of politicians.
And it's why there was such a core portion of the public who knew we'd been betrayed, and so wanted out.
The last referendum was different. We knew the remainer contingent were distorting the truth again, fool me once shame on you, fool me twice would be shame on me, one bitten twice shy, so we paid no heed to the lies.
A payoff to drag us in at the cost of sovereignty in the first place would be quite an incentive to some though. Most plausible.