Politicians don't like to vote against surveillance, because when the inevitable next terrorist attack comes, they don't want to be blamed for doing anything to hinder security.
And, like we saw with Snowden revelations, even if you can expose abuses of the surveillance, the politicians on whose watch it happened don't appreciate the negative publicity for being too permissive or not doing a proper job of oversight. So, they will tend not to clamp down on surveillance, even when shown it's being abused, because doing so would mean admitting their own errors in judgement and failures in oversight.
I guess the only thing that will change their minds is when their own (or their family's) biometric data gets stolen and abused.