Many legislatures may have a tradition of extensive deliberation and debate prior to the adoption of laws, which can postpone passage of necessary legislation.
Thus, in order to pass all desired laws within a reasonable timeframe, they are consolidated into a single bill and voted on quickly, typically near the end of a legislative session.
For example, the Omnibus Budget Reconciliation Act of 1993 was designed to help reduce the federal deficit by approximately $496 billion over five years through restructuring of the tax code.
The Fugitive Slave Act was the most infamous of the five compromise components, and was almost universally excoriated by abolitionists, the chief exception being Sen. Daniel Webster of Massachusetts who prioritized preservation of the Union.
In response, the 1861 Constitution of the Confederate States would ban omnibus legislation, requiring that every bill "shall relate to but one subject, and that shall be expressed in the title" (Article 1, Section 9.20).
This Act changed the law of the land in matters as diverse as homosexuality, prostitution, abortion, gambling, gun control and drunk driving.
The SNC-Lavalin affair, which entailed the censure of Justin Trudeau by the Parliamentary Ethics Commissioner, was started when the firm suggested to Trudeau that he include in his spring 2018 budget bill the deferred prosecution agreement measure that then-Attorney-General Wilson-Raybould refused to sanction, culminating in her January 2019 ouster from government and the subsequent scandal that surrounded it.