Given all the positive characteristics of Venus, why has space exploration focused so much on Mars?

What "positive characteristics" of Venus are given? If you mean a planet habitable by humans, Venus has temperatures to cook meat, plus a thick, soupy, acid atmosphere, and conditions on the surface capable of crushing, dissolving, and melting a battleship. Mars has very little atmosphere, and is cold. If you dress warm and carry a bottle of air with you, them you've got a chance on Mars.

The reason space exploration focused more on Mars than Venus with all the advantages, Venus still has a huge disadvantage, which is that the super hot is there and we can actually land on Venus without exploding.