The compromise should be on the content of the bill specific to the subject. It is not a compromise to allow a rider that funnels money to some pet project. That is buying votes.
Oftentimes there can be no compromise on the specific subject. So the bill is either DOA or just immediately passed without any debate.
Allowing several issues to be passed as a singular unit provides opportunity for an agreement to be made about several issues at once. Think of it like a Collective Bargaining Agreement.
