If you live in America or you hear anything about America, you might have heard about what the media portrays as a veritable river of Mexicans, a Nile of North America, streaming across the border into the US. Some are legal, many are not, and all get labeled with the same stereotype: They don't want to learn the language or assimilate. There is some truth to this, since immigrants frequently do not want to assimilate. They want their old lives but with more freedom and money, though 'by accident' they assimilate almost completely within only a few generations.
One key factor that makes Mexicans stand out compared to other immigrant groups is that they keep coming. This means that at any given time there will be a large non-assimilated population. Whatever the actual rate of assimilation, this will make it appear to be lower. For example, using arbitrary numbers, if 10 enter each year and 9 assimilate per year, that's a very fast assimilation, but it will still result in a 'surplus' of 1 per year. This creates an appearance of a steadily growing population which refuses to assimilate, even if any given individual will eventually assimilate. If there were only a few years of immigration, then once inflow slows or stops, the assimilation rate will take over, but if immigration is ongoing over a long period of time, as has Mexican immigration to the United States, then the reverse happens.
I suspect noobs follow a similar pattern. A new player joins, is terrible, and then we all make fun of him. After a few weeks, months, or maybe years, he is better. But in the meantime, someone newer has joined and as before, they a terrible. We make fun of them, but are wondering, why are there still so many noobs? Repeat as long as needed, until one day we conclude that there must be a large portion of the player population which is irredeemably bad. Since we're not tracking individual players, we cannot see the effects of 'churn', only the apparently constant and disturbingly high portion of noobs.
I left out a lot of factors in assimilation, on purpose, because they were taking up too much of the post and ruining my WoW analogy. If for some reason you want the rest of the post, you can email me for it, but I thought it would be too distracting here.