Different ecosystems work in different ways. In the case of tropical forests the very high rainfall leaches the soil and the biota has adapted to that reality.
Yes
Two reasons. One: that there are environments where building and maintaining topsoil is too hard (eg tropical rainforest) so the adaptive pathway has gone in other directions. Two: humans have been making topsoil disappear since we started agriculture. We now live in an age where so much is transmitted culturally instead of genetically you could call it the post-Darwinian era. This is gross simplification of course because natural selection still takes place as it always has but now many factors interfere with it.
Typically our cultures cannot deal with issues like topsoil because they take generations to see change. When motivation is dominated by the desire to eat today, to make a profit next month and to be elected again in 3 years time how can you spare any thought for problems that have taken thousands of years to develop and will take hundreds to fix?
The way things are heading nothing will be done on a large scale until over population, over consumption, resource limits and climate change form the perfect storm. People will then cry out to leaders saying "why didn't you do anything about it?" The majority of leaders will say "elect me again and I will fix it next year", the few honest ones will say "because you didn't want me to" and they will be the first trampled by the hungry mob.
David