Final answer:
In 1984, the loss of seats by incumbent Democratic judges to unknown Republican challengers was primarily attributed to straight-ticket voting, where voters cast ballots for all candidates from a single party.
Step-by-step explanation:
In 1984, many incumbent Democratic judges lost their seats in large urban counties to unknown Republican challengers primarily due to straight-ticket voting. This phenomenon occurs when voters choose every candidate from a single party, without consideration for individual candidates' qualifications or local issues. During this period, a national trend emerged where voters increasingly voted along party lines in both presidential and congressional elections.
In some states, voters could simply select one box at the top of the ballot to vote for all candidates of a chosen party, which unfortunately often led to non-partisan positions such as judicial seats receiving no votes. This trend of straight-ticket voting contributed to the success of the Republican Party and the challenges faced by incumbent Democrats in retaining their seats.
While gerrymandering and two-party competitiveness certainly have impacted election outcomes and the political landscape, they were not the leading factors for the specific scenario in 1984 involving Democratic judges losing seats.