VGA capable displays ARE common where this thing will be used (racks, movie sets/studios, etc). Plus, those display outputs are for emergencies only as this will always be used headless all the time. You'll get your GUI video output from the thin client connected to that thing over the network.
>I'd expect displayport to be more likely to be added though.
Not in severs. You don't want to waste PCI-E lanes for driving a display output that will never be used and that server chip doesn't even have an iGPU anyway.
Plus, the VGA output is most likely only displays what the motherboard controller is doing and can't display the GUI of the OS running on the CPU.
Also, the VGA connector is miles more robust and fault tolerant than digital outputs where if the handshake fails you get no picture.
Sadly, I think part of the HDMI licence means you can't put analogue outputs on a device with a HDMI port after a certain year. (2014, I think. It was before then that I read that)