Why has the Senate failed to pass a budget when only an up or down vote is needed?

Because Harry Reid will not allow a vote on it as it would hold the government accountable which is something he does not favor

No excuse for it. The House has sent over it's budget year after year and the Senate has tabled it and refused to give it a vote. Even when Dems controlled both chambers, there was no budget, so you can not say they don't agree. If Dems were to put forward a budget they would have to take a stand along with the opportunity to have it ripped apart as laughable. They know by not putting forward their budget and instead just passing bill after bill of 'stimulus' they can avoid a losing fight.

It's all political.

The first answer is wrong, and it appears from your question that you are already aware. Harry Reid won't bring a budget to the floor for a vote. The fear is that a budget might deter the profligate spending caused by Obama and the Democrats.

Reid and the Democrats control the Senate.

They have been a failure of epic proportions.

Democrats up and down the senate are some of the most despicable creatures on the planet.

bugets must originate in the house, not the senate, and though the buget would only need 51 votes, threat of a filibuster makes it 60 votes.

Because it's a useful weapon to use to manipulate and maneuver the House and the American people. If there is no budget there is no constraint to spending.

a simple majority is need to pass any bill..but the filibuster prevents that vote from taking place

Got me. Don't even see how it benefits them. In fact, it makes them look bad.

because sometimes, people don't agree