There are forums about the other areas, but I think there's a few reasons that T1-T2 and going into T3 tend to be the most common. Newer players are more likely to struggle since they haven't learned a whole lot yet and meadows/black forest is where you start out. The black forest may not be the hardest but it is where many new players encounter their first struggles (especially with how misleadingly easy deer jesus is compared to the elder and the other bosses). It's also when many experience their first dungeons, which can also be unforgiving to the unprepared (and sometimes the prepared but unlucky). Compound that with the bronze age grind and the black forest is not the greatest experience for many new players. Then they finally work through that grind and realize that the swamp is one of the steepest learning curves so far in the game but assume it's going to continue the grind (especially after hearing how much iron they might actually need) and I imagine the end of black forest leading into swamp is where most who do give up on the game, decide to do so.

Meanwhile those who do enjoy the game and stick with it continue to learn and adapt and while they may still encounter problems they are also better prepared to deal with those issues so we hear less about it. That and obviously those who do quit earlier on, never get to see these areas in order to post about them. When they do encounter an issue, it's usually something they can also easily look up (like the most common I see for mountain is how to find silver, face large packs of wolves, or beat moder) and they are experienced enough to just do so instead of making a new forum thinking their struggle is unique to them. By later game usually the unique posts involve building, strategies they believe they discovered before others, or sharing interesting moments caused by RNG which are a bit rarer than the frustrations of first figuring out how to play or progress. There's also the potential that the players who are farther along may not want to "spoil" too much for newer players. Sure there isn't much of a story to spoil but a lot of the fun comes from being surprised by your own explorations so hearing about those experiences before you get there can seem somewhat spoiling to some as well.