Because that is not how the LFS demo works.
Non-demo cars are locked to demo racers.. and being locked means that they are unavailable, period. Including using them AND watching someone else in a server using them.The change that has been made aligns demo, S1 and S2 communities. It does not introduce new content to old licence structures. It's important to understand this.
If for no other reason than the posing factor, cruizin past the XFG on the Blackwood long straight in an FXR 

