Why is it up to the democrats?

Because they're the only ones imbued with the power to defeat legislation on behalf of the people who are not themselves members of the fascist cult, though most of them are so deeply in the pocket of fossil fuel interests that they need snorkels to breathe.

Are the us population inept?

Yes, and no. The people in charge of doing things the legal ways are REALLY into stopping people from threatening their power and revenue streams by any means necessary or unnecessary up to and including mass murder.

Even peacefully protesting against oil pipelines is illegal in most jurisdictions and considered TERRORISM in some.

Ever tried to attack a tank battalion armed with just whatever rocks you are able to pick up from the ground, Gaza style?

That's about the power balance between regular people and powerful people in the US when the courts aren't available. Often even when they are.

Assuming you're not a US-ian, you might not know: the US doesn't have any concept of a recall or no-confidence vote like other countries do. Once the election is over, there's nothing the population can legally do about it except protest (which a decent chunk are doing). It's up to the Democrats because they're the ones that were elected by the population to provide a check to the Republicans.

Look, the US is running on a pre-alpha build of representative democracy. We should've updated the system centuries ago, but at this point memory leaks are so out of control and a ton of the cache is mis-addressed, so there's serious questions about whether the thing needs to just be shut down and rebooted in safe mode.

What?

I am an American citizen, this is a democratic republic, the thing I’m supposed to be doing about this is voting, which I’ve done religiously since my 18th birthday 22 years ago. It’s up to the democrats because that’s what we voted for them to do! It’s their literal job!! When you’re the opposition party it’s your job to fight for me, the person who elected you, that’s how this works! The rule of law is far more powerful than I could ever be, that’s why we vote, it’s a proxy for literal fighting. I’m “inept” at literally fighting because that’s not my, or anyone’s role in society I’m very capable of doing my job as a citizen of a democratic republic however, I vote, I write letters, I fundraise, I organize, I used to caucus until my state stoped doing that… my job is to be a citizen not a brawler. I’m doing my job, the Dems need to do theirs.

Yes, they have effectively neutered themselves

Harder to get people to tune out if you don't "both sides" shit all the time and focus on the party not in power for the same reason.