Have you ever wondered why we say "Main Grid" when referring to The Grid? There's only one grid, right? The reason is simple.
Once upon a time, there was only one grid. And it was The Grid. You need registration, specifically a credit card or something similar, in order to log in. And there were no problems. It ran smoothly. You showed your card, paid your dues, and you're in like flint!
A problem presented itself, however. Ol' Phil (or just Linden Lab in general) wanted to get the entire world into Second Life. And judging by the way the Grid was shaping up, it wasn't a kid friendly environment. People had taken a sexual curve to Second Life, and the thought of lawsuits coming down and the Lab's own sense of decency hatched the idea of a separate grid. A dedicated grid. One devoted to children, specifically teens, who could grow into SL while separated from the nasty. And everything seemed settled. You still needed a credit card or something similar to get into the Teen Grid. The assumption was you would ask your parents to register and they'd get the hint you were on Second Life and hopefully monitor you. As I said, everything seemed settled.
And so there came a need for distinction. There were now two grids. The one for kiddies became known as 'The Teen Grid' and the one for adults became 'The Adult Grid'. Phil thought that sounded lame, and people did too, so it morphed into 'The Main Grid'. Nice story.
However, there were problems underlying the Teen Grid from the start. They weren't noticeable at the time because no one could have guessed the future. Hindsight is 20/20. But it was a time bomb nonetheless.
First, there was the fact that Linden Lab tended to ignore the Teen Grid. They'd add the occasional server or two and they got the same updates or so as the Main Grid, but other than that they were left to the winds. In a time when the Lindens were much more active and visible to the population instead of the hermits they are today, few frequented the Teen Grid. The general atmosphere became one of abandonment. The Main Grid was huge, and the Teen Grid, no less in growth, was hobbled with one continent.
Second, children still sneaked into the Main Grid anyway. Parents being parents, kids and teens managed to lasso them into registering their teens into the Main Grid. Some of the stupid ones were caught through sheer immaturity, but a few smart ones evaded capture. Linden Lab shrugged this one off by saying they were taking all necessary steps to ensure kids from being on the Main Grid that were legally necessary, etc etc. Somewhat amusingly, they repeated this line when attempting to implement age registration.
Both of those problems, however, weren't the big killer of the Teen Grid. They were pretty imposing, but easily fixed.
This article claims that the problem and disadvantage of the Teen Grid and why it is dying is equivalent prices to the Main Grid. Shouldn't teens get a break, considering they don't have jobs to support the tier and price of, say, an island? A tough problem, but that's not what has really put the nail into the Teen Grid's heart.
No, this party came to an end when the Main Grid was thrown open into free registration, free of charge and no credit cards required. Just need a name and an email address, and check that box that asks if you're over 18, and you're in! And as the previously linked article notes, the Main Grid is so much bigger with so much more to do. Why take the time and hassle tangoing your parents into getting you into Second Life when you can just claim you're 18 and get into the Main Attraction instead of some sideshow kiddie park?
And as the harsh reality set in, the Teen Grid slowly shriveled. As it sputtered, the Lindens ignored it more often, since the Main Grid was eating up more resources (being so much larger) and why add to it when its growth was barely... well... growing.
Exacerbated by this cold shoulder and the hemorrhaging of users into the Main Grid in the first place, the Teen Grid today is barely known. If you ask the average avatar about it, you'll get a no or a vague reply ("oh, I think I saw that on the main page when registering..."). It's faded into the background as its older brother the big bad Main Grid hogs center stage.
What can Linden Lab do about this? Well, essentially nothing. If you're keeping to the tradition of isolating kids from the harsh adult main grid, that battle has already been lost. If you open the Teen Grid up like the Main grid, you defeat the purpose of preventing the childrens from easily encountering shady elements. If you close the Main Grid off again, you risk the ire of bot owners and regular accounts (who may or may not be potential future paying accounts). It's lose-lose for the Teen Grid.
I think I stated in a post some time ago that LL's attempt at age registration signaled that they acknowledged the failure of their previous attempts at keeping the kids at bay, i.e. the Teen Grid. That was when the Teen Grid was truly lost. It was the Lab saying, "If we can't isolate them, we can try registering them off the 'adult' parcels at least".
And do not tell me that kids aren't on the main grid, or that they're always 'caught'. I've been harassed by guys soliciting sex in such a way that I sincerely pity if it was indeed an adult with that level of maturity. I've seen ages listed in the real life profiles tab that 'Im only 16 so be nice :) :)'. I've had kids outright tell me they are in the main grid looking for the teen scene. If they're not children, there are certainly a lot of pedophiles running around in children suits. Who are trying to pick up other teens who are pedophiles in teen suits. In the bizarre way that only Second Life can be.
In short, the Teen Grid's dead. The only question is when it will finally go, or be absorbed into the Main Grid.