The simple answer is that a whole lot of people really love Setoguchi's writing and are eager to see him return to eroge. Bamboo has also done a very good job promoting the crowdfunding campaign itself.

The trial they released is very compelling, as well. I'd recommend trying it out if you want to see what all the hype is about - it honestly made me feel like Musica could end up being Setoguchi's best work period.