The 'wall' occurs because the super active sphere of fans who will subscribe immediately gets in at the start. Because Hololive has such a huge stake in the western market, once that initial burst is over and done with, there's not really another mass appeal market to tap into and so their growth becomes reliant on the stragglers and new fans. Having all the eyes on them at the start is a double-edged sword because it means their debut is their one chance to make an impression.
Other companies have their own unique sets of challenges regarding growth but the 'Wall' affects Holo the hardest. It's present in all companies that hype a debut cycle but, for other reasons, it's not as bad anywhere else.