This is essentially because the Republicans didn't want to use reconciliation to force a budget through.
Senate rules allow for only one reconciliation bill per year, and they want to use this year's for killing the ACA.
Hence they needed 60 votes to get a funding resolution passed, which meant they needed ten Democratic Senators to side with them. (Why ten and not eight? Because Rand Paul doesn't vote for budgets that don't balance within four years--which this doesn't--and Ted Cruz doesn't vote for any budgets period because he's trying to be "Mr. Conservative" or something. If they'd used reconciliation, they'd barely pass it, because they'd get 50 votes plus Pence's tiebreaker.) And needing ten Dems means that they can't just look to sway Senators like Joe Manchin, Heidi Heitkamp, or Claire McCaskill--they need ones who aren't trying to win favour in their home states by siding with Trump/Republicans.
Combined with McConnell's unwillingness to kill the legislative filibuster, that gave the Democrats significantly more clout than they had on all the other high-profile votes (which were all executive appointments where the filibuster was either gone already or killed in the process).