Why did the large states object to the new jersey plan?

The "New Jersey Plan" for Congress would have given each state an equal number of seats, which means that citizens of less-populous states would have greater influence than those in states with larger numbers of citizens. The "Virginia Plan" was based strictly on population, which meant that smaller states could be rendered powerless compared to those with larger numbers of residents.

In the final compromise, the New Jersey plan became the basis for the US Senate (two per state) and the Virginia plan was adopted for the House of Representatives, where seats are apportioned on the basis of a state's relative population.