[Estragon]

The $5 voucher offered for opting out makes that explanation less plausible.

[hkuo]

Point is that users will more often ignore opt-outs than not, regardless whether it is beneficial to them or not. As a UI practice, it's up to the form's creator how to manipulate this behavior.

[falien]

From my reading I took it that the 5 pound voucher was not mentioned in the agreement, just something they would have gotten after.