Because marriage has always been a matter for the states to decide. And it is not a problem of our own making. Some same-sex couples decided that they were going to to married and overturn thousands of years of practice and all of a sudden it is a big civil rights issue. It sounds to me like the activists and a very sympathetic media are the ones who created the problem. Not the majority.actually, i think it was an issue before (hence all the states passing state constitutional amendments against it and the federal DOMA law). It just wasn't an issue to most because they were on the side that wasn't being restricted so they didn't notice.
And why does it seem easier to 'remedy' things by passing state by state laws and a federal law vs what happened. Of course, that sets aside the unconstitutionality of DOMA. And even if you view that decision as wrong, i don't get why simply repealing it would be more burdensome than your proposal of passing 'appropriate' legislation.
But as i said, a problem of our own making.
Like mac says, it wasn't a problem for the first 200 years of this republic (and thousands of years before that), so why is it now?