Well, Microsoft made some half-assed runs at Orange Book compliance (e.g. Windows NT without floppies/CDs...or networking), but Trusted AIX was a real thing with real users. Having been involved in a couple of MLS Unix implementations, IMO it didn't fall out of favour because no vendor could do it, it fell out of favour because no one could effectively run it in production. The admin overhead of a 'real' TCSEC validate system is formidable, and at some point someone decided 'useable with admins with 6 months of training (e.g. privates and corporals)' was more important than 'checks all the boxes', and the boxes that needed to be checked changed.