They're not voting on that many issues. This is their job, they're supposed to study and try to understand the issues.
And really, this isn't that hard of an issue, I could probably ask my gramma "should AT&T be able to sell your browsing history to advertisers" and she would say no.
The question you're asking your grandma isn't the issue they're concerned about. The quesiton they're asking themselves is if I go against my party, how is this going to affect my re-election. That's why we have party line votes like this. They don't give two shits about the people they're representing, they only care about maintaining office.
