The article you reference focuses on the Jewish ghetto in Venice Italy.
The article indicates that the Jewish community was forced to live on an island in Venice that was the site of an old foundry.There were two bridges that connected the island to the rest of Venice. The bridges and the canals were guarded.
The inference in the article is that the Jews were locked into the ghetto at night to prevent them from getting out, into the other parts of Venice. The rulers of Venice believed the Jews:
"could not be integrated and had to be kept apart"
According to this article:
In Renaissance Europe, Jews were seen as a threat to Christianity.
Although they were viewed as a threat:
Jews were useful because they were prepared to lend to the very poor. The programme tells us that in times of economic difficulty, as in the early 16th century, steps were taken to foster the Jewish community; by providing credit to high risk groups Jews could help boost consumer spending.
The Venetian Republic segregated its Jews to placate the Roman Catholic Church, which had already forced the expulsion of Jews from much of Western Europe. https://europeforvisitors.com/venice/articles/venice_ghetto.htm