You can still reject someone, but it's no longer easy. After you click the Not Now button, you're asked whether you know them, and if you say No they are blocked and can no longer make further friend requests. If you say yes, you can still deny a person's request without blocking them, but you'll have to explicitly navigate to the Facebook Requests page, which isn't easy to find (it's in Friends > Find Friends). With this change, Facebook has turned a one-step process into a multiple-step process that is much more confusing, but ends up giving the site much more traffic.
Since most users are probably not going to bother with all those clicks, simply hitting the Not Now button and forgetting about it, most people sending friend requests will end up as followers. Of course, all the information that is seen by these followers is already public, but this change is making that information visible from their News Feed; they no longer have to go out of their way and navigate to your profile to see it.
This tweak solves the issue of constant friend requests that keep getting rejected, but it creates a much bigger potential issue that some users might not like. This is an excellent time to go review your Facebook privacy settings to make sure they are strict enough so that this won't be an issue for you.