There are plenty of other worlds that are more filled, W6 for instance every K is in use.
But that is W6. Most worlds are 'full' up to at least W30 or so I believe. (Bar a few, W21, W26, W27)
I personally believe the success of a world depends on when and which worlds opened with it. For example, W26 may be smaller, because there was more hype about W25, and not many people were willing to test the new feature.
W27 failed even harder than it could have, because W28's settings were chosen by the public, and more people wanted to play it.
In this case, out of W45 and W46, W45 has become fuller because of the premades which have joined, the hype around it, and the settings.
The same thing is happening with W47. If instead of releasing 2 worlds every 1-3 months, if 1 world was released every 2-6 weeks - this effect might end up dissapearing.