Because Republicans no longer have any power. They lost the Presidency, the House and the Senate. That's why they are going into the messaging of "unity" and "compromise". They have no power.
The only power Republicans have is the filibuster in the Senate. Democrats can, if they want to, eliminate that. Of course, that would probably permanently eliminate it where it could then be used by a Republican Senate.
If Republicans go full in on batnuts crazy and refuse even a comprise bill, Democrats will do that. If Democrats do that, it is over for the Republican party. They will grant amnesty for illegal immigrants with a path to citizenship, grant statehood to DC and Puerto Rico, pass strict election laws, etc. Republicans will never gain power in the Federal government again.
They would also probably restructure the Supreme Court to basically pack the court. Maybe pass universal health care.
Republicans are in a position that if they don't accept reasonable bills, Democrats can and will just roll over them. It would be the end of the Republican party as we know it.