Not my representative, bu Justin Amash, an R from Michigan's 3rd District, posts the rationale for why he voted how he voted on most bills on Facebook.
To my knowledge, he's the only one that does it with any degree of regularity.
I don't agree with many of his other positions, but Congressman Amash deserves credit for consistently standing up to his party and fighting government surveillance.
You can contact them and ask. They're working for you, after all.
For the most part you'll just get a form letter with little to no information in it. It will also almost certainly be written by a staff member that has little to no experience with the policy matter in question.
Responding to a bunch of people individually doesn't scale, so that's not terribly unreasonable. Still, if you call, it does a couple of things 1) you do find out what they think about the issue 2) they know that their constituents care about the issue.
If there isn't one yet, there needs to be one. Our government needs to be made more transparent, and we deserve to know their train of thought for these incredible and large decisions.
If you somehow convince them to require it of themselves you'll just get page after page of disingenuous paffle.
And it'll be done by some intern. Same as when you write or call them now.