The problem is that no leather is totally waterproof, so boots get wet from the outside in, especially at the flex point. OK so in theory leather is breathable, so condensation form your perspiration should get out. It has just taken a while - and is an ongoing process. The advent of plastic boots has given us warm, dry feet, and boots that do not alter their performance characteristics through their life span. The control from a good leather boot can be excellent - but it is almost always at the cost of comfort.
Good plastics offer downhill like support without being uncomfortable.
The inners are removable, so dry out quickly. And they are encased in waterproof shells. There are a few down-sides to plastics. They are still expensive. Good plastics are always more expensive than their leather counterparts.