Why would a Wi-Fi network not support Wi-Fi Calling?
What's now often called Wi-fi calling is actually GAN (Generic Access Networking), so you can prioritize the UMA packets; according to Apple's link you shared above, that is port 500, using IKEv2 over UDP.

"Some types of network traffic (like DNS and IPsec-encrypted) need to be permitted by the network," to get UMA to work, according to a Wikipedia user.

Also, there are conflicts with Apple's Continuity and Wi-fi calling, so it is possible some settings on a Mac or other device at your work are blocking it.

To go deeper, you could find troubleshooting documentation directly into the GAN/UMA protocols.  The site I wanted to reference quickly, Umatoday.com, was down as I tried to access it now.