It's not that complicated: one party is committed to fixing this problem and has influential leaders backing such an initiative. Another party isn't even seriously trying. One GOP senator is interested in solving this problem? Good for that guy, but shame on the other 52 GOP senators that aren't.

> And bills don't represent ideology anyway.

Yes they do, that's why we vote for one party or another. Think taxes are too high? Want to expand social programs? Legislation is how all of that is executed. Bills absolutely represent party ideology. Take the green new deal, for example. How was that bill not an example of party ideology?

> Politicians might be interested in fixing a "vulnerable system" while rejecting a particular bill for some other reason. For example: Voter ID.

Voter ID laws were designed explicitly to suppress minority votes and have been struck down time and again by the courts. They were not designed to solve a legitimate issue, because there is no evidence that rampant voter fraud exists in the US[0].

What does exist, however, are coordinated ballot-harvesting efforts designed to unduly influence the outcome of elections, as was witnessed in NC-9 in this past election. But again, the GOP doesn't seem to be very concerned about this specific issue.

[0]: https://www.brennancenter.org/analysis/debunking-voter-fraud...