I would say that it's the amount of information freely available on the Internet that can be so easily aggregated by using the most basic of tools, such as search engines of any kind, that makes it easy for malicious actors to aggregate information on individuals or groups of individuals and to exploit that. It's not always algorithmically based.
Fundamentally, the algorithms will not work unless the data is available online. Really, the amount of data that most people deposit online wittingly—but mostly unwittingly—every single day is staggering. Over time, there are very many bread crumbs, and the search engines and other tools seek them out and aggregate them.