I'll go out on a limb here and suggest that they are not currently supporting the video codecs needed within the application itself. Video calls can be conducted, but only where the two endpoints can directly negotiate and accommodate the connection without the need for 3CX to be in the middle.
You can always get the 3CX softphone application, load on a laptop with a camera, register and test that way. I did this just last night using the earlier VP-2009P.
My understanding is that 3CX is looking to expand the integration of video more so and perhaps your suggestion should be put into/onto the Facebook ideas/suggestion pages.