They can't reject it entirely, as there are some things that require votes from both sides of the aisle -- those "two-thirds" type votes that are, generally speaking, the most important matters. To trample the D's at all opportunities merely makes them unwilling to go along with R's when we want them to do so.
More to the point, if the Republicans followed your advice, the Democrats could -- with justification -- blame the Republicans for ignoring the good of the country for partisan reasons. Sure, the D's do it too, but they have the media on their side.
This discussion really needs to focus on the political nuts and bolts. Where bipartisanship has generally failed the R's is not on the obvious stuff, but on the stuff that is truly partisan: things like making and enforcing rules, exercise of majority power, and ramming things through (or keeping them in) committee.
Republicans -- especially conservatives -- don't like to play smash-mouth politics. They'd rather assume that the Democrats are as interested in fair play as they are.