Disclosure: I also used to work at D-Cubed, on the 2D constraint solver, but I haven’t for a long time and I’m speaking only for myself here.

Am I the only one to find it crazy that basically all of engineering is using the same proprietary constraint solver that only one company knows how to build?

Perhaps, but it’s a surprisingly complicated problem and at the same time a highly specialised one. Having the big players in the CAD world, who all need to solve much the same problem here, essentially funding a small group of specialists enough to work on it might just be economic incentives doing their job.

I have no insider knowledge about this, but given that D-Cubed was first bought by UGS (a customer, and a direct competitor of many of its other customers) prior to becoming part of Siemens, I expect the lawyers all had provisions in place to deal with any dependency concerns.