The reasons we made the switch are scattered throughout other posts and threads, someone can look at my posts if they want to see why.
However, the biggest reason is console export, which is a feature that will take a while to come to Construct anyway because they don't fully support HTML5.
If we could keep working in Construct and have the same quality, and export options, we would, but sadly we outgrew it.
That doesn't mean I don't recommend Construct for web game developers, hobbyists, freeware developers, and educators.
If the C3 performance upgrade is as good as it looks in the new runtime, C3 will actually be great for the average desktop commercial games too, possibly even mobile.