Just a budget thing. We're still managing our budgets very, very efficiently - Ori and the Blind Forest was made for a tiny budget relative to the project it was. Will of the Wisps already cost quite a lot more than that since way more people have worked on it, but it's obviously not anywhere near as expensive as what publishers are currently paying for AAA games. Our ARPG is the most ambitious thing we ever made. We're trying to be super careful with how we scale so that the company culture doesn't get screwed up and so that we know that we can actually tackle the thing we set out to make.
Fun fact, we could've made the ARPG instead of Will of the Wisps (a prototype already existed by the time we signed the Will of the Wisps contract), but at the time it just didn't feel like we were ready yet as a studio to tackle something this ambitious. Not that Will of the Wisps isn't ambitious, but it was again planned as a bit of a smaller thing than what it became - Now it's this massive 2d game that has production values that are pretty nuts. I doubt anyone is going to match that in the 2d space any time soon, since most studios that aren't set up like we are, it probably wouldn't make any business sense to do it.
But yeah, we're taking the long, carefully planned road here. Moon Studios has existed for 10 years now and it took quite a bit of time to develop the company and make the games we made in order to now be able to make the ARPG confidently. People always only see a studios output, but it actually matters a lot how you build a studio, letting people learn on the job to then do greater things, developing the tools and pipelines necessary to match the next project you want to make, etc. - It's all a LOT of work. The long view here is that Moon hopefully becomes a studio that you can just trust as a gamer, which is why I'm also always taking the time to be approachable and explain in all honesty what we're doing (as far as NDA's let me, that is :D) - I enjoy our culture of no bullshitting, no shallow PR blabla, I want gamers to know that if we release something, it's going to be something special, because we honestly pour our hearts and souls into what we're making. We're shipping our second project soon, I sure hope we'll live up to the high standards we set for ourselves :)