Because openCASCADE is the only open source solid modelling kernel approaching the same league as the Parasolid / ACIS / Inventor / Rhino kernels. Imagine the possibilities if more people had easy access to this level of reliable geometry manipulation. You could use it on the web, for REPRAP type stuff, all kinds of things. Innovation in CAD and therefore in construction and manufacturing could happen a lot faster if you could code agile languages against a good clean and •simple• API for very little start-up cost. Simple is the key word here, I don't see why there can't be a high level API which requires the same level of understanding of solid modelling as using the software through the UI.
EDIT: I was dissing openCASCADE before, didn't mean to.
