Well, firstly don’t expect a single answer, that’s the kind of thing propaganda uses to stop talking about the issues.

The main factors are literal loss of habitats are kinda well known and understood, its just that each little detail has a complex story so asking a broad question doesn’t make sense, and when someone tries to respond to it, the debate takes too long.

We drained line 95% of the bogs, paved over wetlands - these greatly affect more than just the local area, especially since a significant predator, birbs, are migratory, not just seasonally, but immediately too if they can’t find food, so if they can find it a few kilometres away that’s fine), almost no old growth huge forests left, huge loss in plant diversity (eg flowers) directly affects insect population, pesticides and other chemical waste that have different effects, destabilised/unbalanced food chains, monocultures and roads/cities that represent literally an impenetrable barrier for insects and most mamals (so even the shrinking habitats arent connected anymore, and depending on region now everywhere also climate change).