I don't understand. You have hosted two very, very successful games on Steam. Why Steam should refuse a new game of Amanita?
If you have to convince Steam first to host your game, then I would say "goodbye" to Steam. Take it or leave it. Amanita needs more self-confidence in that case...
Amanita addresses that question on their Facebook page:
A commenter wrote:
"Wow just wow ... you already got games prior greenlight on Steam and need greenlight for the new game now?..."
...and Amanita responded by stating:
"...maybe we really don't need the Greenlight process. but it won't hurt. 90€ well spent - Valve doesn't keep it, it goes to charity."