Or people often have their decisions made for them by slightly more tech savvy friends. "Oh, you're using IE? Don't you know that it gives you viruses? Here let me fix that for you.."
But you can't convince people to drop Java if they as much have one site/app depending on it. I'd love to install an alternative non-Oracle Java (not because they're significantly more secure, but to diversify the ecosystem a bit, and to stick it to Oracle for bundling that Ask toolbar), but I haven't figured out how to install them in Win7 yet. (that's not for other people btw, but for the computers at the kids centre I teach)
Still, what I wanted to say, the reason I do give them Chrome (or Firefox, or Opera), is because I'm absolutely unfamiliar with IE, no idea how to enable the proper security settings (or if there are any) and I do want to help many people with an AdBlocker (which also can do wonders for one's Internet security, btw).
There are other good reasons why the security is better, with the only downside being the invasion of privacy, where Google are no worse than others, so pick your poison.