Venus is fascinating but we have no proof that it's not just a deserted wasteland inside and out, and seeing as it would be incredibly expensive to create rovers to explore it, we're pretty happy assuming we've got the story right and we're "done" with Venus for now.
We have tried and tested ways of getting on Mars and it's becoming more and more interesting. (I can't research all the details while this is still relevant, sorry)
The one thing we do know about Mars is that there is water on it, and that's a hell of an exciting fact -- water would be impractical to ship to a different planet, so we can discount human exploration on planets without water. Finally, because Venus is so Earthlike, we aren't really exploring alien territory -- any research we could do there would be easier done here.
I'm in no way an expert, so I've tried to avoid saying facts I can't back up. If anybody can correct me, please do.