Well Venus is very similar to Earth in a lot of respects, it's just got a very dense atmosphere and doesn't have a carbon cycle. Apparently because of the reflective sulfuric acidic clouds, these add around 350 degrees to the air temp.
Ooh, ooh, I know the answer to that one. Is it because they need extremely deep thought and very expensive experiments to get sufficient exercise for those big, Ostrich egg shaped brains that they have?
It's because things like this expand our knowledge of the Universe and help to discover just how it began. In other words, it's to keep a load of scientists in highly paid jobs. Most of them then write books putting forward their theories which can never be proved nor disproved.