Due to a mass of trolling
I have to strongly disagree with this, making new members restricted in no way stops trolling and people posting worthless crap on the forums since the "trolls" are not banned or removed in any way from the main forums. I see what the intentions were but it feels very DRM-esque in its failures in doing anything worthwhile while restricting people who intend on making good contributions.
If i had to be totally honest, OP's post itself actually angers me a little in its short-sightedness and almost verging on a "troll" post itself, which is amusingly meta.
My thoughts on the matter anyway.