Ask HN: Who can explain justifications for these recommendations?

Lately I've seen these recommendations pop up in various threads: https://techsolidarity.org/resources/congressional_howto.html

Given the non-technical audience, and the short, direct instructional nature of the guidance, almost no time is spent on the "why" of these recommendations.

Can folks here help expand just a bit on these, e.g., why use Chrome instead of Firefox, why use Gmail instead of say Fastmail or your ISP's mail, why is Siri not safe to use etc.